I have found 3e CR, 4e monster level, and 5e CR useful tools for estimating a baseline power level for monsters that can be used for judging how tough a monster challenge will be. In Basic/AD&D I mostly went off of what was in modules, then estimating based off of HD, special powers, and getting a feel for the system after years of DMing fights. I never really used the 1e monster levels as a tool, a little bit of the BX HD with maybe an asterisk or two to show special powers. I knew a bunch of special powers could be spoilers in AD&D, especially poison, energy drain, paralysis, aging which were a flag against using a bunch of creatures casually as combat opponents instead of specific story elements, but I got a feel for how well a crocodile or giant octopus would do in fights against the parties I was DMing.
3e got a lot more variables with increasingly swingy numbers and options for variability with complex mechanics from monster feats, adding class levels, templates, and increased HD. CR was a useful tool for getting a better baseline than just eyeballing complex stat blocks, even though party baseline could vary widely.
4e's monster levels were even tighter with their monster math and monsters designed for specific monster roles without using full PC mechanics.
5e is back to similar to 3e, looser than 4e but more to work with than AD&D.
5e's charts pretty much have the bands I want for a combat estimation: easy, medium, hard, deadly. I just find it cumbersome to go through the whole process to get there. Look up a monster's CR, look up separately how much xp that CR is worth, go to the DMG and find the chart for the xp budgets, repeat for each monster that is planned to be used, and then alter the xp calculation for an increase in the number of monsters in the encounter.
So in practice it is fairly cumbersome in 5e to calculate the expected risk of a gnoll leader, a gnoll shaman, a hyenadon, and a couple of gnoll grunts and how much of an expected risk change it would be to add or delete specific monsters from the planned combat.