How about your weapons? I have done experiments on one account I used all rare mechs and some epic weapons and frequently saw legendary stuff the epic weapons were rank 4 and rare stuff rank 3 by the way. I tried it with all rare weapons too, rank 3, and virtually no legendary stuff and if I saw it, it was 2 stars.
I get what you're saying and to be honest, you have a certain point. Weapons are spread across way too many tiers to allow for weapon grades (Rare, Epic, Legendary) to be considered in match making the same way mechs are. The Gear Hub Tiers of items should be considered more than the grades and due to how influential mechs are and how strung out weapons are, mechs and weapons need to have separate influence on the match making.
At the end of the day, here's the biggest issue: You shouldn't be able to buy wins over me (or any player). If the match making system was good, we should have comparable hangers. Right now that's not happening. I'm regularly facing players and bots with stuff I can't get unless I make a cash purchase. That's not fair. I can pretty much guarentee that if many of these players ran my hanger against me, I'd have a really fair and fun match because I'd have to admit that their skill was getting them the win. Right now, I'm facing people that have Tier 9 mechs rounded out with Tier 7 and Tier 8 stuff. That's an entire hanger of legendaries!! At most they'll have Aegis with 4 legendaries. I can't compete with people who are simply out gearing me. I can lose to people who are out playing me, but being outgeared and losing is just no fun.
The Power Rating system is fine, but ONLY IF it is tempered by the tier and grades of the items. A low starred Seeker or Deathwalker (especially Deathwalker) is still no fair against someone who has 1 legendary mech with one legendary weapon and a bunch of Uncommons, Rares and Epics for all 4 other slots (which is my regular setup) - no matter what the Power Ratings may say.
Seriously, this is taking waaaaaay too long to get better. The longer the devs wait, the worse its going to get. Adding more systems (like mods) is only going to make the problem more and more complicated. We are talking about basic things like tiers and item grades. They should be the bedrock of a match making system, not an after thought.