Generally, I see little problem with what you're saying. There appears to be these problems you identify:
1) Too many magic items: however, most don't fit the group, so in the end your group has little magic items to actually equip your PCs with.
Problem appears moot from the get go.
2) Not enough magic items of those found, fit the PCs.
Hmmm. This is related to #1. It seems like this DM isn't about designing magic items for PCs, but more about using magic items as dungeon dressing. Seems OK to me. If you feel frustrated that you find a hoard of items and none fit your PC, think that this hoard might have been absent altogether. Or, if a wand of magic missile was found while there is no wizard if your group, but you found no +2 great axe for your barbarian, then perhaps you can rethink how much of the adventure should shape itself around your PCs. (No offense intended, I'm throwing a line here.)
3) Overpowered encounters
You seem to indicate that your party vanquished the 7 ogres and troll and assassin with super AC. So, was the encounter really overpowered then?
Even if it was, will your party perhaps consider how to approach dungeon crawling from now on, and perhaps change its tactics to move stealthily to hopefully avoid deadly encounters with a dozen ogres and mega-assassins? Or, learn to flee if opposed by a force that is too strong?
Having level-equivalent encounters, every time you meet monsters, is something that is relatively recent in D&D history. Welcome to old school
4) Not enough XP for the encounter
The DM apparently chose a slower level advancement rate. Seems fair game to me.
CONCLUSION
I see little problem in the game you're describing. More, you seem to like the game and its story, which seems like the important stuff.
However, you seem to have a rigid expectation of what the game "should be". I would try to rid myself of that expectation and play the game that the DM proposes. Forget the meta-game: rules for balancing encounters, expected magic item findings, XP advancement rate, etc.. You'll have even more fun.
If there remains something that you really think should be fixed, then you can consider talking to him about it. For example, "you know, Joe, I really like your game. I like the story, I like the pacing, and I like how you play out your NPCs. If I may, however, ask a question: how do you feel about your decision of letting us find a powerful artifact at level 1? Because suddenly, in battles, it feels like we have one level 1 PC artificially boosted to level 5, and four level 1 PCs that trail this guy as a support cast. Well, maybe not that much, but you know what I mean? What are your thoughts about this, and am I missing anything?"