Looping back to where I was trying to start with...a switch to a 4-3 isn't a new architecture, it's changing the guest bedroom from Burgendy to Maroon.
Both schemes have a NT (Clark). Both schemes have 2 edge rushers (Gary and Smith.) Both have two off-the-ball linebackers responsible for run defense, hook zones, and the running backs in man--4-3 calls them WILL (weak outside) and MIKE (Middle) and the 3-4 calls them BUCK (Weak Inside) and MAC (strong inside). Only real difference is most 3-4s slide their 1-2 gaps further to the TE side.
Further, the most common 4-3 in the league today is the 4-3 under, which has been called a hybrid 3-4/4-3 OR "a 3-4 with 4-3 personnel." It was actually Fritz's base look as well. Per the above, go back to 1996. Have Sean Jones play in a 2-point stance. Boom, you're done, it's a 3-4 now. Ditto Seattle under Pete Carrol.
But even with all that, that's still not the biggest issue. The reality is that nickel matters more. And pretty much all teams deploy a 4-2 or 2-4 nickel, as it turns out a front 4 is a better pass defense.
You can play any coverage, cover-2, man-2, tampa-2, cover-3, quarters, cover-1, cover-0 from any front.