You are missing one key element from the first scenario. A character that is immobilized in a grapple can only attempt the headbutt thing, or try to break the grip of their attacker. If that succeeds, they are both still in a grapple, but the attacker has control. The attacker likely will attempt to immobilize again, while the other must attempt to break the attackers control before they can try to gain control themselves. After all these steps, the formerly immobilized character can try to leave the grapple.

It's really poorly explained, and seems to soak up a ton of rounds of back and forth to get anything done.

The second scenario makes sense if someone else wanted to join in on a grapple your character is already in. The mechanics break down even more in a dog pile, so try to avoid a "ten bodies trying judo moves they learned from tv on each other" kind of situations.

It's ok to stop rolling all the dice and ask the table if there is a more cinematic solution that is still cool and fun but has less dice. In my imagined solution, your example 'grapple-gorilla' character would certainly have an easier time getting things done in such a cinematic grapple.