Another Mew question
We can only get one mew, right? So, there's no reason to *not* power him up, even if not ideal?
I still have a while to get there, but just curious for whenever I do.
Answers
Nah just get another Espeon, they're not too hard to get, walk literally any high level Eevee and it'll be better than Mew in the situations where you'd want to use an Espeon.
Espeon and Alakazam have 2 purposes, for use against Machamp and Gengar raids.
Both of them do Machamp quicker, and despite the lower survivability have more damage per life because of their higher attack and stronger movesets. Mew at 40 is barely able to win vs Machamp in theory, while Espeon / Alakazam are only behind Mewtwo.
Against Gengar there are some advantages for Mew, as it has better damage per life than Alakazam / Espeon but still requires it to be around level 30 minimum just to get it done on time.
The investment required (rare candies, stardust, and both types of TMs) just to make Mew even acceptable in raids - not even "good" - is too high for what it provides.
Middling stats and difficulty in getting the moveset you want are reasons to not power it up.
Sure you could turn it into any type attacker, but for most players they could just get the best (or best non-legendary) Pokemon of that type and it would perform better and cost less TMs, unless you're fortunate enough to already have the moveset needed when you caught it, which is very unlikely given how many possible moveset combinations exist.