The typical arrangement in a multiplayer game was that you would have a division of labour. Romania in the Axis with marines for example, carrying out the naval invasions of the Mediterranean. Their divisions may have been 100% special forces, yes, but when viewed against the faction the % share going special forces was still low.
Now, a nation like Romania will never be able to use special forces, they don't have the mass of infantry to support them, and there is nothing that their teammates can do it about it. Instead, the big countries like Germany will have even more on their plate, having to manage Marines and naval landings as well.
Its not strictly realistic, but HOI4 is a game. Now, conflict will be a lot more stationary, with less movement of territory and more static defense. There will be more reliance on planes to just do the killing that infantry can no longer do. Its a backwards step. Events like DDay are hugely satisfying when they work, but the reality is they rely on masses of marines. Now, most attacks will just flounder at the sea unless backed up by an insane amount of CAS.
44 Widths, Field Marshalls and Special forces were killed off in the name of historical accuracy, fun be damned!
Overthrowing Hitler from inside and Communist Japan were added for fun, historical accuracy... be damned?