I think the theory on the Samurai is Japan routinely showed up as weak so a crazy strong unique unit helped it out. War Chariots for Egypt are also a little nuts on strength too. I'd be fine reducing the strength to some intermediate space where it's a buffed longsword with some promotions myself, but the set strength as it is (not precisely where it is numerically, but it being linked to the musket strength) goes back to mid-GEM at least. It's not a bug at any rate.
I have no idea where the destroyer-carrier-destroyer path as an idea even came from. But it's absolutely dumb. The arque isn't sensible either. It's at least plausible as something to upgrade from pikes. It can do that anyway without merging it into the GG/MG line though.
I think the issue there is that the vanguard promotion set is still distinguished from that of soldier units (medic vs siege say), so the unit paths need to be available. If we abolish the distinctions, the "vanguard" units still have value as they're non-resourced, compared to swords and horses, and can have defensive promotions or anti-mounted/anti-tank counters to make them useful in combat while still being effective anti-city options with access to siege. I really don't see the point of making a dedicated healer line of units that also can't attack cities effectively. This makes the units too specialized and removes choices from the game from the player. I should be able to use spears/pikes to attack and conquer with some ability if I'm short on iron, say, while they still make excellent screens for archers and catapults alongside swords if I have them. I should not be shoehorned into making them into defensive screens that heal and having to rely mostly on archers, catapults, and ships to attack cities. I think this is the hold-up in changing the land-unit paths.
If the issue is the AI is making too many healers to be able to fight aggressively, give them more XP to pick something else or see if the promotion AI can be altered to give it a lower order of priority over strength bonuses that help attack or hold ground first.