AaronOfBarbaria
Adventurer
Not really. I mean, you might bend the numbers so that they match where you want them to match, but figuring out that you have a party of PCs that average a CR of 24 (an example number chosen for no particular reason) doesn't actually mean anything useful, or that they are going to consider a CR 24 monster a significant enough threat to maybe fight it alone.But at least this way they are both equally inaccurate, so it balances out right?!
Mostly because CR-figuring includes assumptions that aren't true of PCs - especially in the offense category, since expecting a PC to unload their biggest "guns" in the first 3 rounds of combat isn't an expectation likely to be met on a regular basis, unlike with monsters who have no reason not to do that very thing. Plus if the party does meet that expectation, there is a solid chance the next encounter won't have as potent of fire-power to start it off so you either have an even less accurate CR (the one assuming their most potent abilities), or you have had to refigure the PCs CR for each benchmark at which they just don't have enough resources remaining to be their earlier figured CR.
You are incorrectly assuming a difference between my method and being a good DM who knows the party and the adversaries thrown at them.And of course your suggestion isn't really a method at all. With stats up to 30 from boons (or just alternate progression I forget which) there can and will be a large change in difficult as the PCs gain more boons. So some method would be good, but it will never beat a good DM who knows his party and the adversaries she is throwing at them.
Maybe I shouldn't, but I assume that anyone getting characters up to 20th level is going to know what they are doing by that point.