No auto-roster-fill with bots in Customs?

I may be misunderstanding what the Bots can and can’t do…but I thought that, at least in matchmaking, if you have a 4v4 Arena match, and a minute into the match, one player drops out, they would be seamlessly replaced by a BOT until a replacement player can be lined up…

Why can we not have this option in Customs?

Biggest problem I am finding with the new Customs Browser is TEAM IMBALANCE.

I can either start the match with an empty lobby, and HOPE people show up…OR…start with a full lobby of BOTS, and as real players show up, they just ADD to the list of players until we go beyond the intended player number, or just cannot join because the max player count is already met…by the bots.

Why can I not just start up a 4V4, with me and 3 bots on my team, and a FULL TEAM of bots on the enemy side, and then just have the bots drop out as real players trickle in?

Am I alone in thinking this would’ve been part of the Customs Browser all along?