SMN is fine.

If you want to be optimal just play BLM and SMN so you have the option to switch if one suits a fight better.

Generally people like BLM in prog due to Apoc and (to an extent) Manaward/wall. However, due to BLM's playstyle, they also usually require catering and specific strategies developed to optimize their DPS.

SMN provides traited Virus, Raise, mobility, and ~*DoTz*~.

Basically, none of this matters if you aren't shooting for world first, but I'd recommend leveling both just so you have the tools to help your group if they need it.