Or rather, it really depends on what your threshold is for classifying something as same or different. And there's no point saying it's gone if it's still there but changed.
In all the games I played, RPG or not, I can't think of any profession class character or thing that comes closer to the GW1 mesmer than the GW2 mesmer in role function and gameplay. GW1 mesmers were hard to describe as well because shutdown roles are fairly rare in games even in RPGs. Debuff is more common, but shutdown? And mesmers have a variety of ways to shutdown, e.g. e-denial, interrupt, punish, skill failure... I feel GW1 mesmers were truly unique and defining of GW as a game that innovates. GW2 mesmers is the only thing that comes close to it.
By comparison, the guardian is pretty hard to describe as "it's this or that profession or class" or even "it's a combination of this and that" because even paladins are quite different from guardians in that the former rely on healing allies (or being frontline) and the latter on applying position-based prots (and being frontline). And it's very different from prot monks in that you're hard-shelled and mostly frontline.
So if you want to play prot monk in GW2, I don't know what to recommend (guardian? water ele?). If you want to play guardian in GW1, I also don't know what to recommend (dervish? prot monk? paragon?). But if you like mesmer in either game, then mesmer is the closest match in the other by far.
Much like engineer is the closest match to ritualist, you know, aside for the look and lore, and assassin is the closest match to thief, aside for the look and lore and balance.