I have no idea if anything like this has been suggested, but here goes. 

Instead of how Hanger Showdown maxes out every mech and weapon you have based on stars, have something where no matter what mech and weapon that each players uses, it either takes the average of everyone, and scales down or up everything so it's all the same power. Or to take the lowest SP and lower everyone to that SP level. There can be levels like HS has, but base it on how many of each common, uncommon, rare, epic, and legendary mechs and weapons that you use. Or even have each level set a certain SP point that everyone would have.  For example:

Uncommon Level 5: 2,000 SP

Common     Level 4: 4,000 SP

Rare             Level 3:  7,000SP

Epic              Level 2: 10,000 SP

Legendary    Level 1: 15,000 SP

Each level can have one or 2 mechs or weapons from the higher tier. This should help stop SP dropping and make a pretty fair gameplay.

Feel free to add suggestions that could make it better.