I mean...that's pretty much true, right? 5e isn't properly balanced, many of it's fans will state that this is either a feature or that it's a great thing that the DM can fine tune balance for their own tables. It makes it hard to discuss the game in general with others because each table is different, and each DM handles (or doesn't) the system in their own way.
There is no amount of short rests that is balanced for every party. Some require 1. Some require 2. Some require 3. A party of, say, 2 Battlemasters and two Celestial Warlocks, with no limit on how many rests they can take, can practically adventure forever.
Meanwhile, an all-Monk party might have to short rest every 2 encounters. A party of 4 Clerics might never have to short rest at all.
And yet, we're told that 5e isn't a game where you need a specific class composition to play. That any four dudes can tackle 6-8 encounters between long rests with (presumably) 2 short rests.* And with no assumption of how many resources the party has at the beginning of each encounter (other than, I assume most of their hit points), no assumption of a particular accuracy or AC, only "how much damage can they do" and "how much damage can they take".
There's no way you can make a game able to run out of the box in this fashion. It is absolutely on the Dungeon Master to make this work.
*Assuming this is actually the metric used by internal design, of course.