"Solo" is quite hard for any mage since they require buffs and recharger, but that's another thing.
Speaking of SPS alone meh. They are not bad, their cast and crt rate is higher than other mages...and they're not bad in PvP either but when it comes to 'farm' they're quite the worst.
SPH and Necros both learn CDL which is a HUGE skill that helps you farm way easier and faster since you can kill with 2-3 nukes mobs that are, otherwise, a 6+ nukes deal.
Also, they has no vampiric skill that can save them from death if they need, they are forced to use 'battle heal'.
Aaand in the end, they learn real AOE skills quite in the late-game at lv 58, while SPH learns Tempest at 46 and Sorcer learns Blazing circle at 40. To be 'fair' SPS also learn "Frost wall" at lv 50...but the cast range is 40 and it doesn't have a worth 'radius'...sooo...
Damn, looking at it from this POV i really picked up the worst freaking mage to play, lol.
Probably the only one who may be 'worse' than SPS is necros 'till 50 when they learn CDL 'cause they have no aoe skill (just one at lv 46, but you need to cast it on a dead-mob), they have Blaze from lv 35 up 'till lv 44 where they learn Death spike...but even there, Death spike requires bones which are quite expensive...and when mobs drops 200 adenas, you really need to 'save' as more as you can.
So from the PVE point of view SPS are really trash, for a reason or for the other...
When it comes down to PVP it's quite different 'cause your casting is faster than ur opponent and also, you can learn Ice dagger that bleed ur enemy. Now, back in the days i used to cast ice dagger first and the hydro blast 'cause i was able to cast 2 skills while my opponent was casting 1...and ice dagger could stop the enemy cast. I tried this in giran, and even tho i quit the server at lv 57, it never happened. Looks like nowdays it's rare to block a cast without a critical hit, and even in that case, you may not break it. Meaning that ur only "strong" point is ur casting speed and m critical rate.