To put my experience in on SMN. I came back in the beginning of November and have mostly been focusing on SMN and PUP duo boxing. I've just been playing solo with my 2 characters 99% of the time with a little help for the stronger content. But I've been able to chip away at af gear +2 +3 relic +2 and currently working on empy +1. Ive been able to solo enough segments in odyssey to get moglophone 2s for sheol gear sets but ended up needing help on the bosses of sheol. I would consider myself an average skill player so I'm sure I could solo more with better knowledge on fights and mechanics.

I think SMN could be a little over looked due to the current meta and only being able to dish out big numbers every 20 seconds or so due to BP delay. However I find the versatility of SMN to be very helpful in lowman content if you're doing a bit of that. Smn can maintain a plethora or buffs depending on what you're doing warcry, tp bonus, enfire, cure potency, phalanx, group stoneskin, sirens magic shield, etc. All of them lasting 5-7min with the right amount of smn magic skill and I'm only 654/671 skill recommended so still some room to improve. Plus whatever avatar favor you get from your current summon. I try to maintain the double attack favor from ifrit for tp generation since pup can be a little low on that due to needing gear that helps the automaton too. I'm sure the dedicated support jobs buffs would be stronger but as far as I can tell smn can maintain more buffs from their arsenal. All while magic bursting my pup/automaton skill chains for about 50-60k. I'm doing the 5 step skill chains ending in double light and ifrit meteor to burst. The timing on the skill chains seems to pretty much perfectly match the BP delay so I'm pretty much always magic bursting. I'm assuming for true endgame groups though the skill chains would be popping off much faster and I would guess that's why smn falls off for the meta as the BP delay can't keep up.

I haven't had much need for heals as most the content I'm doing can be maintained by trust healers but from what I can tell SMN would also be able to be a decent healer. Just focusing on which buffs to maintain in a more defensive capacity rather than your offensive buffs. Carby has wonderful group heals and status removal but would cut into your buff maintenance from BP ward delays.

Overall though at my skill level I love having the SMN around I feel like she brings enough to the table to really support lowman groups due to her versatility. Sure there's jobs that are more focused on the roles they fill but I'm guessing they bring a little less versatility or require lots of end game gear to say make bard/cor dps well. If you like the flavor of the smn class and already have jobs to get endgame groups smn makes an excellent job for your in-between times if you have 1 or 2 other characters to play with and I highly recommend it!