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

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And that's me 4,523

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Who would you prefer to meet?

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

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Doesn't have enough bloody mechs for it :)

That is all just my opinion.. 

"As an example look this guy"

This made me chuckle. This player is in my award playoff grouping (the one with pilot Sunny as the main prize), along with other heavy hitters and top 500 players. Not much chance of me getting top 3 this time :-).

Like @Papa said, SP is definitely a factor for regular games (non tournament, non hangar showdown). But in the past the devs have indicated there are other factors like your win rate. So subtle things may change who you face and we don't really know what those things are.

They always say to balance your hanger to get like opponents. I have tried that for quite a while and it never works. You have to trick the system somehow, another thing I never seen to learn how to do, to be able to get equal or lesser opponents. They don't talk about what exactly their matchmaking takes account for, and they never will. 

I have 2 accounts, and with both of them I have had to go against others that have had over twice my hanger power. My main runs a hanger just shy of 6k, yet I go against 12k+ quite a bit. The highest I have gone against was a little over 20k, but it has been a while since that one.

There is no trick other then the one being played on you. As you have read in the other posts there is no real good system in place. The reason is the game is FTP/P2W. The free part is to get you playing and the paying part is to shortcut advancing you hanger/mechs. In order to get you to pay they have to make you feel you need to advance your hanger to compete. The issue is it doesn't work. You advance and they still put you against more powerful teams. Unless it is your turn to be the winner. The way they help achieve that is be using Bots(mech AI) to influence the match outcome. 

So just play to have fun, spend if you want to, but unless you get endgame mechs/weapons(BIG MONEY SPENT)... You will have the same playing experience of what appears to be unbalanced matches.