To start, Dragon could probably use a spawn timer, hes basically a boss and should respawn like it. Make him drop more scales, maybe a couple more items, and let him take a break.
Especially if he can be solo'd, and sometimes easily. Wth SNS and Hellfire tonned down, the next problem are summons. Summons start out as just very useful ways of having meat shields for your soft magely meat flesh, but when the summons are growing both in number and power they scale out of hand quickly. If you can beat a dragon with a single Skill line, it needs a second glance.
Summoning itself is fine, it could probably be its own class in fact, with spells that revolve around buffing/manipulating summoned pets, but as a 'support' its more like a way of doubling a characters power. (A level 92 wizard would be killed if all 6 of his fairies turned on him)
Today i tried to solo ice dragon without using summons, it was slow and difficulty and risky and a couple deaths were had, but with snares, poisons, and a lot of hit/run/hiding it was doable, and thats fine.
Throwing pets at the dragon and winning is not, fighting the dragon WITH your pets just makes him die faster.
Last night a group of us faught the ice dragon, 3-4 of us, we got all our equipment, and we planned it out. We'd hid it, we'd run if we got focused, we'd snare him so we could escape, we wore him down. It was risky, slow, and really fun.
Today, Khor and Tanker put on some of their best gear, got everything ready, and we were able to put the ice dragon down four times before depleting weapon charges and such. Tanker the White Knight tanked, Khor the Black Barbarian DPS'ed, it was quick, it was sometimes dangerous (not a predictable fight) but it paid off. We decided we'd do it again sometime, and thats fine.
Taking 800g of reagents and turning it into a dragon farm is not fine. This kind of goes into the Wizards lack of gear dependency. Tanker and I both risked our fancy equips, risk and reward.
So, what can be done. Summons are a constant affect, having them out could cost an amount of SP/MP. So you can have your army but your characters primary abilities will suffer for it, in some situations this is useful.
Higher tier summons could just require more slots, so instead of 6 fairies you could have three, or 2 water elementals. 3 fairy > 6 earth elementals anyways.
Summoning could be a class of its own, or added into Druidry and left as a Neutral Magic. Wearable items could augment summoning, like +1 minion on your chest, helmet, boots, gloves and reduce the base amount to 1 +1 from title.
'Necromancer' is a popular class in most games, especially if they have minions, this should be a tree that allows for a higher minion count but not as powerful ones. Maybe a choice of one 'general' undead and a squad of ghouls/skellies. Something that could be cleaned up with good AoE though.
White Magic could have a couple summons put in, like summon a floating sword or an archon, maybe take a knight skin and make him glowy and holy looking.
Dragon AI could be better to ignore pets more, or get some AoE skills to combat them better. If boss is going to be solo'd it must be a challenge and require a good amount of equipment, or nothing is risked.