I'm old enough to remember the lesson that former Majority Leader McConnell taught us, that if you have the power to do something, then there's nothing wrong with doing it. Changing the filibuster rule isn't "breaking the rules" its just amending them to your party's will. https://twitter.com/LeaderMcConnell/status/1352317412226568198
No one is going to give 2 shits about this discussion in a month from now. Dems don't need to give this "agreement" to McConnell for nothing in exchange.
He's threatening to break a norm if Dems don't agree not to break a different norm at some point in the future. He doesn't give a shit about either. He knows the odds are small that the committee allocation rule he's threatening will ever matter while he's still in office.
He's also betting that nothing is lost if he just gives Dems the right committee allocations, but why not try it to see how gullible Schumer is. No chance he holds the line on the allocations b/c it'll further tank GOP approval among independents.