Struggle/squirm, in replacement of resist for the non-dominant grappler.
This would be an exhaust essentially giving up trying to get out of the grapple in favor of trying to minorly wound or exhaust the grapple controller as much as possible. However with enough agility or strength, this would be able to be mostly ignored. This would allow someone with much higher levels of endurance to essentially force a draw or over on a strangling situation, by exhausting the target enough that strength wasn't enough to contain them. At which point, the grapple breaks.
Seize control, in replacement of resist for the non-dominant grappler
A compared agility and strength check, to seize control and take the position of grappling leader. Essentially someone may outmatch you in the department of strength, however you might have them beat in flexibility by a lot, allowing you to get behind them and get them into a choke. This hold could then be broken with struggle or control could be seized back, however you would have delayed their strangle until they could do one of the two.
These two replacing the current resist would basically add an interplay, do you want to go for control and fuck with the asshole grappling you, or do you want to exhaust and eventually get out? They also add more stats to the equation than Strength.
Replace the grapple controllers automatic strangle in combat with a switch, between
Punish, deal bruising and minor exhaustion compared to choke. The damage from this would be based on agility. And punshing would leave you more vulnerable to people taking control of the grapple.
Choke, Deal minor bruising to the neck and head, and major exhaustion compared to punishing, Enforcing the stability, but leaving you more vulnerable to the grappled person exhausting you quicker with squirming and breaking the grapple sooner.
This adds a byplay and reactivity to the usage of grappling. And brings it closer in line with the reality of grappling IRL without bogging it down with too much systemization.
Next I have two ideas for essentially moves to pull off, just two ideas and they are superfluous to the main point about grappling, and they are based off professional WWE style wrestling not sport wrestling. As sport wrestling is basically a martial art of it's own. But basically these moves would be overmatch disengages, ones that would show the person who you are grappling with that you're very much beyond them.
Suplex, you're grappling with someone, overmatch them heavily, and suplex them, pulling their head into the pavement and injuring them.
Throw, another overmatch, though on of a lesser degree than a suplex, essentially prone someone and deal minor damage while disengaging the grapple.
Grappling is not just a factor of strength IRL, it's a measure of coordination, flexibility and application of that strength. The addition of additional options for grapplers is a good idea, as it adds flavor and complexity to what is ultimately a very simple system currently.