Part of the argument was that since modern aircraft use many of the "features" that the 109 did then the 109 must have been innovative.
Which is more a bunch of coincidences that piled up over the years rather than true leading the way on part of Messerschmitt team.
Like the leading edge slats.
See:
rolls-royce goshawk | napier dagger | bristol perseus | 1934 | 0631 | Flight Archive
for an article about 16 prototype machines that were displayed to the public at Hendon in June of 1934, almost 11 months before the 109 first flew.
at least 7 have leading edge slats (partial span) to help maintain aileron control near or during the stall and prevent/control spins which were a big killer in WW I and the 1920s.
The use of partial span slats was very common at this time and for a good reason. Modern jets use moveable surfaces on the leading edge of the wing. But these surfaces do not have the same purpose (spin avoidance ) and a lot more to do with lift enhancement in general. To credit the 109 and it's design team with "leading the way" seems a bit much. I don't fault Messerschmitt for using them, many design teams were feeling their way forward trying to combine good handling and low drag and other requirements. The 109 followed one path, other design teams followed other paths. At the time several of these paths could be correct as long as they produced a good product.
Landing gear attached to the fuselage as innovative.
As shown landing gear had been attached to fuselages almost since the beginning of flight. It made for a light structure. It also meant that many of those Biplanes could be towed around with the wings off. As landing speeds went up (and airfields stayed unpaved or poorly paved) and large engines/props had increased torque effects, wider landing gear became a benefit. With the coming of jets and their thinner (relatively) wings hiding the landing gear in them became more problematic. In order to use skinny tires that would fit in the wing the English Electric Lighting used tire pressures approach 300lb pr sq in and many early (and not so early jets ) were concrete runway only. That and the wing (being on/near the center of gravity) became an even more desirable place to store fuel and the landing gear took up a lot of room.
The idea of towing jets around on their landing gear with the wings removed pretty much disappeared
the adoption of multiple hard points under each wing also conflicted with the space needed for landing gear.
With jets going to mid-fuselage wings or high mount wings the length/weight of wing mounted landing gear grew. Mounting the landing gear in the bottom or bottom corners of the fuselage became a more attractive option. The designers of the 109 had their reasons for mounting the landing gear the way they did. Modern jet designers have their reasons for mounting landing gear the way they do. They are not the same set of reasons although light weight and compact are certainly considerations.
The center gun argument.
The very first fighters used single machine gun, with 80-120hp it was all they could carry without seriously degrading performance.
As engine power went up for firepower (2nd gun) could be added.
During the 20s somethings stagnated. Two machine guns was considered sufficient for several reasons. Planes didn't get that much tougher or faster.
Increases in engine power were somewhat offset by increases in weight. A 400hp Jupiter engine weighed close to 800lbs compared to the the 500lbs of a 230hp Bentley Rotary. The bigger engine required a bit more fuel and a stronger airframe. Engines and airframes got somewhat more durable but their wasn't a lot excess power for large increases in gun power (although some of the guns did increase in rates of fire.)
With the coming of the cannon, which the French pioneered, the early engines didn't really have enough power to carry two cannon. Not to mention the ammunition feeds were bulky (box magazines or drums) which would not fit well into the wings.
By the late 30s engine power had picked up enough that 2 cannon were possible (if they were light) and they got the guns to function (mostly) laying on their sides which helped hide the drums. Cycle rates were low however. In 1940-41 belt fed guns with higher cycle rates became available and a single such cannon offered a fair amount of firepower (backed up by several machine guns) but the bombers had gotten a lot tougher (bigger) and a single 20mm was no longer enough. Multiple 20mm guns (many of which could not be synchronized to fire through the propeller) became the desired armament (if not always obtained)
With a few variations four 20mm guns seemed to be nice compromise between desired destructive effect and weight of guns and ammo for the plane to carry.
These are generalizations, there are a number of exceptions.
Post WWII with even bigger bombers (B-29s and TU-4s) carrying nuclear bombs called for much more destructive armament than even the four 20mm guns and faster firing guns, bigger caliber guns (or both) became standard and the missile and rocket fad started.
ending up with things like this
1/2 the armament on a F-89H. No guns left.
Vietnam and few other conflicts showed the missile/rocket armement didn't work as advertised and many planes got a gun (or two) stuck back in as back up to the missile battery which sucked up hundreds of pounds of weight and many cubic feet of fuselage space with the electronics.
But going to guns only was no longer an option as it limited a fighter too much. Most people settled on a single fast firing gun as the back up. There wasn't weight or volume enough for more than one or two fast firing guns. which wound up back in the fuselage for number of reasons, one of which is that they don't fit in the wings very well.
even turning it on it's side won't work
Of course even in the 1950s putting a heavy gun battery in the wings was getting difficult
Modern planes are designed they way they are for reasons. Perhaps some of the reasons coincide with some of the reasons that a plane form the 30s was designed, perhaps not. claiming that a 1930s design showed the way or was "innovative" because modern aircraft have a superficial resemblance to the general layout/configuration ignores all the changes in between and why they were done.