lichmaster
Hero
From my experience, many encounters in official 5e adventures suck, big time.I didn't design that encounter. It was in a published adventure, and I ran it as-is, with the details provided, and the tactics the author gave.
In RoTFM for instance there's an encounter with an alleged CR6 Frost Giant Skeleton that can oneshot crit any character at the level when the encounter happens, and it can come with a hag.
That's only the last one outrageously bad encounter I experienced, a year back, as a player.
I do run published adventures for many of the same reasons you're mentioning, but I do significantly change encounters (either when prepping or during play) because by experience just by looking at numbers I can see all the pitfalls. It's surprising sometimes that older adventures (pre 5e) were much better designed for their own edition than current ones, in my experience.
3PP adventures may be way better though.