Would this trading system work for D4? It combines free trade with BoA

It will always be so as long as players can copy/paste stuff - you’ll have illusion of choice and illusion of being clever. This can change only with a next gen randomization approach that makes all the variables unique for each player changing these each Season. Needless to mention the skill cap hits the sky then and you’ll have cry babies all over the place since they can’t copy/paste the meta, but you’ll be rewarded for being clever and finding the meta in your own context.

You have power tiers regarding builds with builds in each tier balanced among each other. The optimal efficiency play is to hit the top tier build for each activity (related to D4 - each Key Dungeon) as fast as possible. So, you have both balancing and a reason if you aim efficiency. If you aim fun, well yes, you play whatever you want - no need to change the default skill if you have fun with it.