The issue with morale is it's a force multiplier for the team that's winning.
I think it should be renamed something like "focus/character/resolve" or something. The "starts at 50" thing I like. Then, it should work opposite of how it does now.
The more bad stuff happens, the more focused your player/team gets. So their bar increases slightly. On the opposite, the team that's winning loses some focus and relaxes a bit. The more good stuff that happens, the more they relax.
Then, you can invest in whatever the renamed skill for Heart is to help prevent this "loss of focus". Likewise, it'll help a team that's given up a play gain focus.
Then, from 50, you either gain or lose some skills based on how close to zero or how close to 100 you are as has been mentioned. SAs like Trash Talk, Prime Time, Celebration, etc... all still make a ton of sense. They're things that can cause your player to lose focus or resolve. They'd need a balance pass for sure still so they're not so powerful.
Changing morale in this way would generally help the teams that are losing and slow down the teams that are winning. Then choosing to invest into heart(renamed?) or intimidation/toughness would enhance your ability to leverage/avoid this effect depending on your situation.
Summary: Morale shouldn't be a force multiplier for the winning team, it should be a mechanic that assists the losing team in catching up. Superior teams would want to invest into the appropriate skills to guard against it's impact. Inferior teams would invest in those skills to try and leverage further it's impact.