Title says it all, that limit is just frustrating for no reason and gets on the way of content creators willing to share Teams with the community.
If for whatever reason this wouldn't be something to consider because of ingame code, UI or something here's an alternative:
Make 2 sections, one section of 5 Teams available for play.
and another with Unlimited Teams (called here Library to make it easier).
Imported Teams automatically add in the Library. Players can at any point drag and drop teams from the Library to the Playlist and vice-versa.
Edit 1: Another idea with still improving the QOL of the people building Teams and playing our game that was submitted by @tranquil vapor down below would be a Duplicate button, so that players can test alternatives of their team without screwing the original. It's ok if we need to make a separate post for this idea, a mod just let us know but i think both can/should just be implemented together