Please do not use this experience as an excuse to make everything ridiculously hard. There’s a lot of planning and thought that goes into a PC; seeing it all pay off in an encounter like this is what makes the game fun for most players who can pull this off. I’m not saying every encounter should be over with in 2 rounds, but I think it’s better that every encounter is over in 2 rounds than if every encounter has a dead PC. In my experience, too many GMs think that their job is to beat the PCs when their job is to lose in a contest as close as they can manage.
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I wholly share your sentiments on the last line, although I would amend it to “… when their job is to make the game fun for everyone in it while advancing a coherent narrative.” Sometimes, that means making the fight as close to a TPK as possible without actually causing a TPK. Sometimes, that means allowing the PCs to just destroy an encounter like legendary heroes in movies. I see it as being somewhat like a Marvel movie: sometimes you see the Avengers smashing through hordes of dangerous foot soldier enemies, and sometimes they fight Thanos. But the movie wouldn’t work if all the fights were one or the other: it’s the combination of the mook beat-downs and the wow-we-nearly-lost-there fights that makes the plot work.