im not an expert, and nobody knows for sure what matchmaking is, apart from developers, because it's not open source, but in my opinion it's based on hangar power, it doesnt care if you put rare mechs or pilots... every mech, weapon and even pilot or mod has power rating.. this totals 1,893 power for your opponent as on your screenshot.. 

So it takes the power of all your mechs and weapons in a hangar and then it will probably search for at least 1 available human opponent as close to that number as possible and fill the rest with bots...

Funnily rare or common mechs will have same power rating as legendary.. only stars would matter.. but legendary weapons are usually higher on power ranking.. pilots or mods dont add much, but if you want to be really low you could take them off.. So if you want easy games, you could either make it fairer, by putting legendary/epic mechs, but rare/common weapons... or you could make it stupid by putting one legendary mech with good weapon and the rest the least stars mechs you can and the most common weapons you can.. but basically check total power rating of hangar after every change to see for yourself.

I think in worst case you will still get an enemy with 2800 power hangar even if you have 1500... it doesn't feel very fair and strict.. but on average it should work as intended. Does not mean meeting a hangar with 1000 power is better than meeting a hangar of 2800 power. 

As an example look this guy: 92971814

The power of 1,324 (4433 wins out of 4532 games) HA HA HA

i

i

And that's me 4,523

i

i

Who would you prefer to meet?

Although one thing im sure of, he can't f do this:

i

Doesn't have enough bloody mechs for it :)

That is all just my opinion..