Of course your character is powerful. He has five dots in Mind. That's a big fuckin' deal.
First of all, you should go to Shadownessence.com, register and ask your questions there, since it's the best WoD community around.
Secondly, your ST is ignoring the real problems with magic, which are threefold:
1) Countermagic and wards are very important. Mages are unique in their ability to specifically counter each others' efforts. If your sanctum isn't full of wards and bans, you can die quite easily.
Related to this are rank 1 senses. If your enemy uses magic, he can find out pretty much anything about you.
Finally, any cool thing you can do an NPC can do.
2) Extended rituals are extremely lethal. Your enemies should be picking up traces of your Effects, tracking them back to you, and then building up a good 15 successes or so to obliteate you from the face of the earth. You should be building your defenses, which leads to:
3) Limits on running effects. In the old rules, every two Effects (rounded up) running increase difficulties for all subsequent rolls by 1. If you aren't using this rule, there are going to be balance problems.
So your choices are to nuke people and float around until somebody kills you, or to carefully balance your personal defences with your ability to act.