DIP is nice too for annexing vassals. With vassal integration act you're getting 1.4 DIP per development (actually a bit less, looking at in-game totals), worse than ADM for territorial cores but good enough to make use of a secondary point type + offload OE.
It's MIL I don't care about too much in the end game, since I'm finding with +3 siege era bonus that I sit on 100% OE regardless of whether I'm using it for artillery barrage. However extra MIL can be used to push more RT, effectively transferring MIL into a bit more ADM/DIP. You can, in effect, nearly always re-elect unless a ruler is very old.
Disinherit can get you the 7-9 point average in ADM/DIP from ruler, though it is harder to concentrate that into ADM (which is more efficient this late). Having a ton of prestige available from not disinheriting does also open up possibilities like just straight up vassaling Japan that has territory off its islands and buying down LD, or making a 500 development client state and flooring its LD quickly.
It's good that AI won't cancel cores in progress now. I gave a Chinese client state 15 unrest worth of overextension, set it to scutage, paid off its loans, and after 20 years or so it actually managed to get cores done. Always make sure to use great power influence on these things since it gives them monarch points.
The ability to pull subjects this size and manage them easily makes me downgrade the value of PUs after early game...very few meaningful PUs get near/over 500 in development. In the end game, you're fighting these nations.