I mean, that describes most RPGs. But it doesn't really describe 5E well, because it, like a minority of RPGs, is more interested in attrition. Indeed 5E may be the most attrition-oriented RPG out there. Most of the others that do this are either D&D-relatives, or, interestingly, narrative games like a lot of PtbA/FitD games (not all of them), or Resistance-system games (Spire/Heart, for example)*.
I gotta be honest here, it sounds like you're playing D&D perfectly normally and just bumped up from Normal to Hard encounters, presumably because you have a well-optimised/organised group of PCs/players, but labelling others who don't do the same as having victory literally "served up" to them on a "platinum platter", is just weird as hell given that.
Ok, let's try a different approach...
I am challenging the players (regardless of their experience with the game) with combats, many of which could turn deadly given any number of circumstances. IME this is what the game would call a Hard to Deadly encounter. Assuming typical play choices, dice rolls, etc. The players know they will likely be victorious 90% of the time (the 9-in-10 from upthread), sometimes with more attrition--sometimes less. 1-in-10 times either I throw something at them (Deadly) to remind them that victory is not a guarantee
or bad choices, bad rolls, etc. do it for me. In such circumstances, the PCs "fail to defeat" the encounter and are forced to retreat, surrender, negotiate, etc. FWIW, this ratio is of course not set--just a relative goal I try to reach by judging the pace of encounters, where the adventure is heading, etc.
Anyway, If I don't do that and house-rule the game, it [combat] is really a piece of cake (on that platinum platter) given those default guidelines for encounter design, etc. you mentioned. IME most games after 5th level become academic if a DM follows the encounter guidelines and/or doesn't have house-rules to counter the default system. Combat in such games is boring and predictable IMO.
FWIW, I am not going to discuss this point of the game being designed in easy-mode as that topic has been done so often it is ridiculous at this point. If you disagree, no issues, but that is how I see and have experienced 5E and so I stick by it.
But all that being said, if a player finds combat boring (because they
simply aren't interested in it) then it begs the question: why waste your time with combat since the PCs win (by default) practically all the time?
(
Now, this is making an assumption about the combat experiences of a group-- do you find combat boring in general or because you win all the time? The OP does not specify why they started the thread, so my response was to @overgeeked who from their post finds combat boring because of the foregone conclusion of victory.)
If you want a random system just in case you desire an element of risk and possible loss, then do a single roll (as I described upthread). Or, do something like
@overgeeked suggested (a single combat check for accumulated damage to determine the victor). If keeping attrition in the game is important to you, there are lots of ways to handle it with a simpler system than combat.
Or, you don't worry about attrition (unless it plays some factor in your single-roll system?) and just narrate every combat accept perhaps the climax encounters... which is what I was originally suggesting to
@overgeeked if regular combat is tedious. Because even if you develop a single roll system, my first thought is such a system will
still be boring because it will be designed for the PCs to continue to win most of the time--because that seems to be what people want? (It is certainly how 5E was designed...)
Ultimately, I like to think of it like this:
Do you want to do a word-search game or a cross-word puzzle?
Both can certainly be fun, but the first practically assures you of success if you give it enough time, while the second you might struggle a LOT to finish--if you even can. If combat is like a word-search: relatively easy and something you can always complete but you find that boring, your options are either try a different style of combat (e.g. cross-word puzzle) or don't bother doing the combat (and spend your valuable game time engaging it what is more fun for your group).