We basically got half an update. The restriction of the hero needing to be on the team to earn champion xp will go hand in hand with the hero not really “being” a certain class all the time and only having that class be active when that hero is actually on the team. But we didn’t get the other half - making it so that any class of hero can be inserted into a team at any time and it would stick to that and being able to freely insert any class of hero into the team. That is the part that is tricky and potentially game breaking to implement.
The 50 gem fee to change classes as is stands now is simply unpleasant design - they don’t want people to have to go through several menus to change the class to put a different class hero on the team and they know that people want to, so the fee is there so you don’t even want to in an attempt to (poorly) steer you away from such a glaring design flaw. One could argue that, and I would tend to agree with, that this is even worse, though.
(Go to 40:35 if it doesn’t take you there.)
I personally think that a 1 hour timer is plenty of “friction” to keep players from hyperoptimizing and needing to go into these menus constantly. This is short enough for a stretch of casual play focused on one task before switching to another, and long enough that you aren’t going into the menu every few battles.