Note: If you treat your companions like your family this post is not for you
What I usually do sometimes to intentionally knock my companion unconsious. Like going to the bone drakes in Avernus and having my weakest companion as my first mate, put him out front, and get knocked out. After that I flee immediately and don't go to the life fountain. This may not be the best thing as it can be time consuming and a long walk if your beloved companion gets knocked out in the process. Though it has worked for me and Romba and Old Scratch are still out of play. Just be sure not to get most or any of your best companions knocked out after. Cheers!
Yeah I think since you end up getting many companions it's hard to keep up with them, they are like puppies that you have to feed all the time, but in this case they eat training points. I don't think that giving up a companion like Old Scratch away, who is important to the story. Maybe for crowns KI could make a potion that allows you to pick your companions for one battle, just like an epic battle? I think that would be a nice idea.
Maybe we should be able to buy training points in the crown shop too! So we could buy a bunch like 12 or 15 for crowns instead of just using gold to buy one point. I just entered Monquista and I see my companions levels slipping a little.
Actually, I have over <1% companions and they rarely show up, probably just my luck though. I ended up soloing Mooshu and here and there I got a bad companion though. I remember one time I was fighting a hard boss at the end of a dungeon and I got my worst companion who is level 17; Crazy Monquistador. Luckily he criticaled and did some decent damage until he was murdered by a pig. Luckily I had El Toro and Mustang Sally I believe, but I pulled through! Quite intense though. I like this game because it requires strategy even if you may not have the strongest crew.