And to say you can find it plausible that Volgin can live on because of his lust for revenge on Big Boss, but Liquid can't because of the same reason is contradictory in itself.
Of course I didn't like it, but that's why I'm giving my reasons why that is so.
Volgin's body was left intact, and experimented on, it wasn't just his "lust for revenge" that made him function the way he did (it just kept him living in a comatose state). On the other hand, Liquid's arm was literally transplanted onto Ocelot and this was actually taken as a serious plot point for the character unlike Volgin's where it was just put together because it was somehow cool.
It's a case of being able to write ridiculous things while keeping things at a certain tone. The Cobra Unit is the perfect example of this, where their ridiculous antics are treated very separately from the whole deal with The Boss's self-sacrifice. Liquid's arm is tonally jarring because it relies on this similarly ridiculous and contrived premise while actually making the viewer take it seriously. It's that tonal difference in the writing that seems to escape people here by blanketing the whole thing under "Kojima's done more crazier stuff" when there are cues in the mood, story, and voice that serves to illustrate the intended framing of a situation for each character.
Ocelot's crazy gun tricks aren't something that majorly affects the story either, he's literally that one cowboy guy who does cool gun tricks. In this case, MGSV is treated like a horror circus showcase. We have Skull Face (cowboy skeleton), Mantis (creepy psychic child), Volgin (Frankenstein's monster), the Parasite Unit (super parasite zombies), all of which are purposefully written with a horror-like undertone for the sake of cool and creepiness. While MGS2 certainly had its share of ridiculous moments, most were treated in such a way that the story didn't actually hinge on them (is Vamp running on water just as much of an important plot point as Liquid taking over Ocelot then?).
The thing is, those things were written in such a way that they either didn't factor as a serious plot element or there's an obvious intention in the tone that uses them to the fullest effect (like MGSV being paranormal/horror-themed). The problem was that Liquid's arm did none of those things. We were basically meant to take the whole thing seriously as if it's somehow natural for Liquid to manifest in Ocelot through a single transplanted arm.
Nothing in the writing, mood, or story, indicated the sheer ridiculousness of it. It wasn't even treated as if it's like some crazy horror-type idea, Liquid literally just came back through an arm because he was apparently popular and Kojima regretted killing him. That right there is cartoon logic.