"From time to time" is the critical part of that nothing wrong. When "time into time" is more like "nearly all the time" things start coming apart.No, you miss the point. There is nothing wrong with single encounter adventuring days from time to time; you're expected to mix it up as a DM, with some longer than 6 or so, some shorter than 6 or so, some with more short rests than 2 some with less short rests than 2 adventuring days.
On different days different classes will shine. More encounters and more short rests favor Warlocks, Monks and Fighters. Fewer encounters will favor Paladins and Casters. Many encounters and few short rests will favor Champions and Rogues.
It's intentionally designed that way so a DM can play around with class balance by simply adding in short rests, or encounters (or taking them away), and to also remove the 'sameness' that bothered a lot of people in 4E.
The spotlight can be moved around and shared, by simply adjusting your encounter and rest frequencies.
There is no holy RAW that says anywhere 'Thou must do 6-8 encounters and 2-3 short rests'. It's just the classes and encounters are balanced best around that figure. You simply use that as a median or baseline, and design your adventuring days for your Party around that, with maybe shorter days, longer days, more short rests, fewer etc as you see fit.
To see how its done, look at the 15th level Adventure I'm running on this board (to test out high level play). A simple Doom clock has kept the players on task, forced them to be careful with resource use (HP, slots, action surges, SP etc) and imparted a much more strategic level of play to the game (i.e. not just button mashing), while also driving the story forward.
Should the players succeed or fail they'll also feel like their actions matter (and they do) to the story, and what they do has consequences.
Edit: before saying "well dont do that as a gm" level that at wotc in their adventures teaching new gms to do exactly that