Nothing you have said here is not equally true of mutually exclusive UNWs and UIs build by UGPs also have their own stats and artwork. In the case of UGP making a UGPTI, the two components in question aren't even the same category.
But fine, edited the OP to drop the GGalleass. The Fusta is now a standalone unit that is weaker and cheaper than the base galleass. If Venice has to sacrifice either coverage or conventional strength then it can get by without the conventional steroid, but consuming 2 separate component slots to cover a single base component is absurd.
I think removing the Great Galleass in favor of the Fusta is a massive mistake. Playing a game on the latest version, I believe the only change needed is removing the Fusta instead. Venice in their 2UC form seemed to be one of the best civs in the game despite their shortcomings, and was the only civ I've tried and succeeded in beating deity difficulty with. With 4UC they still seem to be top tier, and the Fusta either doesn't change that much at best, or can break mechanics of the game at worst.
Main concerns / arguments against the Fusta:
1. Having a cheap unique unit that doesn't require supply or maintenance allows the player to abuse several mechanics of the game.
The final Fealty policy (Fiefdoms) can be broken by buying up loads of ships (possibly with faith via the Zealotry belief) in the renaissance/industrial era and keeping them out of sight until the endgame, obtaining infinite happiness. There's also implications for policies like Freedom's "Arsenal of Democracy" which gives a bonus to unit gifts, and can be gamed by hoarding these units too. If any other policy or belief is changed in the future to scale on unit count, this will remain a concern.
2. The Fusta doesn't serve it's stated purpose of defending trade routes.
In my experience Venice generally doesn't have a difficult time defending coastal shipping close to home, but ocean shipping farther away, which the Fusta's low CS and slow ocean movement make it a poor fit for. Barbarian caravels aren't countered particularly well far from friendly territory to heal, and In the event of a major war most shipping will be pillaged in enemy territory you can't access immediately, in ocean space you can't completely observe, or directly near cities not well defended.
The Great Galleass far better fits this role as they are individually far more capable and Venice can still build them after researching navigation. They can have a capable, non-iron ranged ship to defend coastal areas, which frees up valuable frigates to patrol the high seas as you look to secure more Iron before industrialization. Also, one Great Galleass can monitor an area for longer without healing and better counter barbarian ships.
Edit: I forgot frigates no longer required iron. They are still cheaper to produce/buy than frigates while still holding their own in the era, start with Bombardment I (giving higher quality frigates on upgrade), and are more effective at sieging in some scenarios due to being able to move after attacking, so I still think they fill a defensive and offensive role better.
3. Venice's chronic war supply problem is an important counter to their power.
In a similar way that India's inability to make missionaries allows them to have unique religion mechanics without being broken, Venice's supply and unit production constraints check their unique trade and puppet mechanics.
There are already multiple ways for the player to address this dilemma with their current kit:
- Investing in unit quality rather than quantity via infrastructure investment, wonders (including their own unique wonder), culture policies, and leveraging the Great Galleass.
- Increasing supply via conquering and buying city states, conquering less defended coastal cities, and settling Colonia (which I think is no longer capped?).
- Avoiding war/pillaging in the first place via allying neighbors and city states.
The Fusta doesn't change Venice's dilemma, it just breaks the calculous for a short period of time and makes decision making less interesting. I would say if the player winds up in a scenario where the Fusta is their only option, there were many mistakes made before to get to that point (though I'm not convinced that's even a likely scenario). I would say the same if someone had a dire religious situation with India that they thought only missionaries could solve, but I doubt that is a likely scenario either. There might be an argument that it's useful to make the AI more competitive, but I don't think that outweighs the potential mechanic breaking by the player.
If you read all that, thanks. Venice is one of my favorite civs to play and I want them to remain in a good place, especially if 4UC's going to be integrated moving forward.