This maybe your problem, the level 4th brute is not a level 4th brute to a level 10 wizard, but a level 4th minion at least, most of the time it should only be a narrated encounter with no actual dice rolling.
You keep missing the point that opposition is relative to the players, and by the time they are level 30th most players will actually be fighting hordes of level 25 balor minions as they try to kill the BBEG who is an elite or even a solo of the relevant level.
It's all relative.
I get it, I just think that it is fundamentally ridiculous that the game world has no actual numerical reality until the PCs encounter it. IMC the 20th level lich is a reality (numerically and narratively) whether the PCs are 1st level or 23rd level. The whole relative reality is exactly what games like Elder Scrolls: Oblivion does with its dungeons. The world morphs to meet the PCs where they are. IMC and in most people's campaigns that I know, there are places that are appropriate and innappropriate to wander into because if you enter a region where powerful monsters exist and you are weak (and ignore the warnings) you die.
Personally I do a lot of narrative things in my own campaign like cut scenes and other narration to immerse my players in the game. However, the very idea of everyone of a certain level able to one shot, with spell or weapon, enemies who have historically and thematically been powerful like devils, giants, ogres, etc. getting snuffed out in the midst of a fireball that wouldn't auto-kill creatures of half that level objectively.
Of course there is no creature that would be half the PCs level within the boundaries of PC reality that would not be a minion and that every creature of lower level than the PCs is open to one-shot kills. If there are mezzodemon minions for PCs over a certain level then is it even possible that any creature of lower level isn't a minion? Anything is possible, but is is possible to make any actual sense of it outside of absolute gamism...I don't see it.
No, this all depends on the GM style. If the narration of the GM is purposely cartoonish, then you will have a silly adventure. Note that this can happen with any edition of any RPG out there. So no blaming bad GMing unto the rules.
In a world where suddenly halfling rogues can one-shot kill hill giants with a 6 inch dagger potentially one after another then I think we have crossed into a brave new world of potentially silly realities. Putting a DM into the position of having to, in order to be fair, allow the halfling to potentially do what the 6ft. 6", 250lb barbarian wielding a greatsword can do because of the minion rules is nuts. It's hard to houserule certain realities without completely hosing the players and screwing the pooch in redards to the rules.
Even where minion rules can potentially make sense such as with mighty warriors haking through squads of red shirts, 4e has it were everyone is potentially Conan, even Wizards because everyone has to be equally badass in combat even if you are a 60yr old man who spent his entire life reading tomes and writing scrolls....If a DM doesn't consider Kill Bill and Jackie Chan movies vivid portrayals of heroic action in the classic sense, these rules are a problem.
Wyrmshadows