Oh gee, where to even start. Not that it even matters, if you haven't listened so far you're certainly not going to start doing it now. Still, might make me feel a bit better to vent, even if it's into the void.
"...it is the most flexible parameter..."
Well, I'll give you that one. I mean, it can mean literally anything, so sure, it's flexible. Of course, you can also replace "flexible" with "inaccurate", and it'd still be true.
"...useful to match roughly compatible players from the pool of a wide range of opponents with varying activity and experience"
No, it's not. It's useful for matching players with comparable power levels, nothing else. What that power translates to differs wildly, and activity and experience has nothing whatsoever to do with it, and compatibility certainly doesn't. What matters in arena matchmaking is arena performance. Every single game I can think of with matchmaking does this. I have yet to see a single even remotely valid reason for why this game couldn't. The only possible excuse I can think of involves the arena being so fundamentally broken that you've explicitly chosen to do it this way in order to hide it for as long as possible rather than actually put some effort into fixing it, or accepting the fact that your idea of "competitive" is nonsensical and setting aside those delusions in favor of creating something that is actually fun.
"For instance, though the status of the Great Hall..." etc.
Well, I agree that the upgrade level is not an accurate representation. That being said, it's still orders of magnitude better than player power, because at least it actually reflects some aspect of your potential power, whereas player power could just as well be from filling up your vault with common champions for food.
"Of course, as many of you pointed out, our current approach to the matchmaking (with account power being an important but not the only factor) has some limitations and drawbacks."
You don't say? Such as literally punishing you for playing the game for any other reason than the arena? This isn't "some" drawbacks, it's literally a system that counteracts the fundamental principle of the entire game. You have created a system in which I actively avoid keeping champions around, and keep champions unequipped because they may only be useful in one area of the game where I would instead accept suboptimal teams in order to maintain my arena ranking and give some semblance of efficiency in getting medals for the great hall that even in the best-case scenario will take years to complete. I long for the day I can maintain a place in and win a reasonable amount of matches in gold (I'm able to get there at the moment, but winning matches is a full-time job), but not because I really want the bonuses from the tier or the gold medals particularly, but because it means I could finally, finally, escape from this horrendous matchmaking system and actually start enjoying other aspects of the game such as faction wars.
I don't know which prospect I find more disturbing. That you have no clue what you're doing, or that you do and that this is what you actually wanted.