As far as the Lysander goes, it was useless in it's intended role/s. No amount of use in other roles is going to change that. After being a total flop as a combat aircraft (or trying to exist in a combat zone) it saw a lot of use as a trainer, ASR, target tug and 'agent' dropper.
It probably would have been useful enough if produced in smaller numbers: cut down the Lysander orders and up the Whirlwind orders early on and production rate of the latter should have increased substantially.
IF that order had occurred prior to the Peregrine's discontinued production during the 1940 production rationalization, engine demand would have been higher earlier and production might have ramped up enough to put out a good deal more peregrines and possibly even address more of the problems sooner. (larger orders + more money + more interest tends to expedite things)
Part of the poor efficiency of peregrine production in combination with merlins may have been the low volume and overhead it would take to ramp-up production or maintain low volume production vs the merlin already ramping up and gaining efficiency. (In the unlikely event that demand was high enough to merit expanding Rolls Royce's manufacturing facilities sooner, it definitely would have changed the trade-offs for rationalization as total volume output would be higher than it historically was in 1940 and peregrine and merlin production could be kept in separate factories with specialization efficiency optimized for both)
They didn't have a problem producing both the Merlin and Griffon later on.
Of course the Peregrine was the lowest power, it was the smallest engine. Another "detail" that isn't important apparently. The Peregrine weighed 1106lbs for a power to weight ratio or 1.25lbs per HP. A Merlin X two speed engine running on 87 octane had a power to weight ratio of 1.26lb per HP. granted is the power to weight ratio of the complete aircraft that counts so the smaller engine is at a disadvantage there.
Actually, I may have misspoken earlier regarding the V-1710-33 (C-15). I know the F3R had a dry weight of 1310 lbs, but the -33 was lighter, I just don't know how much. (if it really was about the same weight as the Peregrine, it might have been a good swap to make, though the radiators would need to be enlarged or maximum power restricted -might also run into idle overheating like the P-40)
Napier building V-1710s is an interesting idea, but I suspect there might be production tolerance issues given the standards for typical (existing) Napier vs Allison/GM manufacturing. (I know Ford of Britain had tighter standards than Rolls Royce and made similar changed as Packard to facilitate production in their factories)
Hand-fitting Allison components was used on some of the AVG's P-40s using rejected engines salvaged using hand-machined/fitted components to work around the out of spec tolerances, so it might not have been a problem other than reducing efficiency compared to GM/Allison and making parts less universally interchangeable ... and maintenance more difficult. (no worse than existing Napier or early-war Rolls Royce engines)
Importing V-1710s to supplement Napier/Rolls/etc built Peregrines might make more sense as far as timing and cost given that Rolls and Napier collaborating/licensing seems more likely than Allison/GM and Napier. (or Ford of Britain, except the V-1710 might actually be faster to set up efficiently with Ford than the Merlin, though bureaucratic and trans-atlantic communication overhead would slow progress -and you need foresight to start things in motion early either way)
F-series production would mean an end of lighter engines to import, so Allison would be a dead-end in that respect.
Lots seem to go back to 'peregrine or bust' for the Whirlwind ... with one final exception for the V-1710-33:
it's powerful enough to be useful on the Spitfire while lighter and better streamlined than the Merlin and better adapted for 'tropical' conditions without using those awful external filters. And without changing the weight or structural integrity of the engine, Merlin XX/45 style refinements to the intake manifold and supercharger housing could improve altitude performance a fair extent and improve power at all altitudes due to improved efficiency (better mass flow, less heating, charge density) while staying within the conservative American ratings. (RAF style stressing and overboosting aside -which it would tolerate much less than the F series anyway, but maybe compete with the Merlin III, and possibly more aggressive 30 min, max climb, and max continuous) Maybe a good engine for Spit V trop? The weight and drag savings would probably be wasted on the Hurricane, especially with its finicky CoG.
In ANY of these cases there's one other key point:
The Air Ministry needs to put higher priority on the Whirlwind sooner and significantly expand the number of aircraft ordered in 1939. (without that, Peregrine demand stays low, as does any interest in alternate engines)
BTW, I am still waiting for accounts of those Peregrine engine failures that were due to fundamental flaws in in the engine. Either design or quality control.
No one has called me out on it yet, but would my supposition on this matter be accurate given the information available:
The Taurus and Saber were both more fundamentally flawed in design and/or mass production methodology/quality control than the Peregrine was. Same goes for the vulture, while the Peregrine in 1939 didn't seem too far off from Merlin development/performance characteristics given the size.
That and, in terms of R&D resources, the peregrine would have shared a good deal with the Merlin and Griffon, just on a smaller scale. (unlike the greater differences in the Vulture design, or the interesting but very different Exe)
The bigger stretch might be an argument that, even in 1940, canceling the Vulture and moving on to a coupled/double-V or H-block engine more directly based on the Peregrine would be a safer bet for a reliable 2000+ class engine in a timely manner than the Saber or Centaurus. (and faster than trying to license any American engine technology in that power class)
If they were as much trouble as some writers have claimed (not just on this forum) the wonder is that they used them as long as they did. Beaufighter might have had a bit more trouble with the overland low level strikes. Whirlwind was as fast or faster than some early Spitfires at low level. It also had good roll response which is an advantage in tree top flying. Not trying to take anything away from the Beaufighter but you are comparing a 10,000lb airplane to an over 20,000lb airplane and while the Beaufighter was certainly versatile and did a number of jobs well, low level strikes in contested air space may not have been the best place for it.
The good roll response is also an outstanding feature to have on a twin engine fighter given the large wingspan and high outboard mass. (better indicating potential competitive nature vs single engined fighters)
As far as competing with the Beaufighter, it's a bit apples and oranges there (the Mosquito would be better suited to displace the Beaufighter in heavy fighter-bomber roles) but that said, the Whirlwind SHOULD have gained better heavy load and shorter take-off capabilities with those slats sorted out and a bit more engine power. The point would more be competing with the Typhoon and P-47 for fighter-bomber capabilities, or P-38 ... and easily outperforming the Hurricane and P-40 in that role. (I can't imagine a Whirlwind Mk.II wouldn't have heavier wing rack ratings AND drop tank capabilities AND fuel cross-feed -lots of detail changes to fix the shortcomings of the Mk.I, and changes far more realistic and practical than switching to engines several hundred pounds heavier)