Except that court packing is a purely partisan play where they gain nothing from not reciprocating in kind, whereas they benefit symmetrically from a reduction in executive power for the same reason as you -- it helps them the next time they're in the minority. And the symmetrical move wouldn't be to re-grant those powers to the executive, it would be to further limit the executive from unilaterally doing some things the other party doesn't think it should be doing.

The best case scenario would be to somehow get both parties actually targeting the other's corruption instead of just trying to get the votes needed to be the ones sticking the money in their own pockets.