The Hispano engine was the height of technology..................in 1931.And yet
1) the D.520 proved to be a viable fighter which did pretty well in engagements with Allied types well into 1943 and
2) there were many other 12Y variants with increased power, despite what you always say against it. The French seemed to be pretty confident in not just the 12Y-50 and 51 but also the 12Y-77 and 12Z which did actually get into small scale production (in Spain) though the Spanish were not able to sort out teething problems.
The French actually had very little choice unless another company came up with brand new engine. They were trapped trying build Hispano engines on existing machinery. The 170mm bore spacing goes back to the 300hp Hispano V-8 of 1918.
One of the things the Swiss did was increase the weight of the crankshaft from 50kg to 80kg. The Hispano engine's crankcase and crankshaft were not strong enough to stand up to the power that the customers were looking for.
The increase power variants always came with major changes in structure and weight. The Hispano needed a change from two valves. and it needed a bunch of other changes.
The 12Z got 4 valve heads and gained around 140kg (almost 30%) in weight.
The Russian M-105 got 3 valve heads and gained around 80-90kg in weight. also gained a two speed supercharger drive which helped boost the low altitude power.
They also reduced the bore size to strengthen the cylinders.
The Swiss Saurer YS-2 gained 190-200kg to get 4 valve heads and other improvements. Result was
1300hp for take-off at 2600rpm.
The Swiss ended with the Saurer YS-4 that used a variable speed supercharger, Bosch fuel injection, 100/130 fuel and a weight of 1555lbs/705kg (43% increase) for
1600hp/2800rpm/46.7in (8.6lbs boost) take-off
1580hp/2800rpm/ 15,300ft/4600meters Military power.
even later in timing. Swedes post war were building DB605 engines that gave 1475hp at take-off and 1575hp at 7,000ft on 91/96 fuel that weighed 725kg for perspective.
The Hispano had been passed by in 1939/40 and the only countries that kept it had lot invested in tooling.
Look up the problems the Russians had with the V-106 and V-107 engines.