That is interesting: what if the Gm gets "Doom Points" based on encounter numbers disparity? That is, the ratio of PCs to monsters (as the encounter is designed) equals the number of Doom points/LRs the GM starts the encounter with. So if it is 4 PCs against a boss monster and its lieutenant, then the GM gets 2 Doom Points.
I've done this in my games. Some bosses get one or two doom points (I call them "dreadful blessings" in my game and they're usually tied into the story like having the Blessing of the Nameless King or the Blessings of Ibbalan). Bigger bosses at higher levels get more. I wing the amount but once I've decided on the amount, the players
know how many there are. I have little Shadow of the Demon Lord tokens I put on the table. Online, I make it clear how many doom points a boss has and how many they've spent.
Because I can basically use doom points for anything, I end up using them faster than legendary resistance (they replace LR for my legendary monsters). This means players can see them being burned faster than normal, which they like.
Before using doom points, my players essentially ignored them and just didn't cast anything that they worried would be affected by LR. But now, they're willing to burn them down because they burn down fast enough that it's worth while.
I've used them now in three different games at tier 2 and tier 3 and my players have pretty much universally liked them. They get the point of them and find them less annoying than pure LR which is interesting.
Flavor-wise, I have some in-world flavor for them and I don't feel like they're forcing a story. Instead, I feel like the save or suck spells are forcing the story out of whack. Powerful shouldn't be trivial encounters. That's the break in the story, not letting them remain powerful and threatening. Powerful and threatening
is the story.