William being in the closet was for jokes. There was never much depth to it other than forcing himself to date Atom Eve and Eve getting frustrated with him not even caring they broke up. flying him around princess style was kind of funny.
Either way, it made sense back then why he was in the closet. Now it wouldn’t make sense.
If you read the comics the only fatigue was some “are they dead?! NO THEY’RE ALIVE”. Although it wasn’t actually Allen that caused these issues.
Invincible suffered from the opposite of what you fear the boys and Marvel are doing. The comic story was moving too fast and near the end it feels like Kirkman was trying to rush the series out the door. Think like GoT last seasons where you were getting whiplash from armies teleportating.
Fatigue Is more a thing that happens when a show or series is going nowhere, or there is just too much of it. If we were getting 30 episodes a season it could happen, but 8 episodes 2-3 years apart? That’s not a big problem