But the most easiest and best way to solve this problem is...to just not use 20 mechs.
I know it's within the right of players blah blah to use mechs and whatever mechanics that are provided by the game blah blah but you do realize that the hardest part of agreeing to a rule is to have communication between guilds, and, surprisingly all of you agree and acknowledge this without being offended/blaming others.
With the hardest step and part gone, you could all simply convince your guild to use a non ridiculous number of mechs. Of course at some points some guild will start using 10 billion mechs again despite the mutual agreement, you could all bash on that guild's castle and let them get nothing. Or just think of something else.
Just simply saying, you guys already skipped past the most difficult part of creating a mutual agreement so why not make it real. We all know that skill change nerfs like these take a long time and may not even ever happen, so why not stick to something realistic and possible that's right in front of us right now. Use something like ~6 mechs and actually concentrate and have fun with your main character in WoE.