Some of this pushback saying 5E is designed fine (across the board, it is implied or read), because it works for so many people, are painting things with as broad a brush as those who are saying 5E sucks (across the board, it is implied, or read). There are several factors in the game's design and history that make it "work just fine"—or not—for many people:
- 5E's massive growth means that for many people, this is their first & only role-playing game. They have no basis for comparison, it is just how RPGs work, in spite of particular problems with specific parts of the game that could be designed better.
- 5E is D&D, and D&D has a huge amount of brand prestige—and product support—which is a good part of why so many people play it, newcomers, old hands, and grognards alike.
- The more casual the player, the less likely they are to care about design (and vice versa). 5E is built for more casual players. It's much simpler than AD&D, but It does still have a lot of complexity. As with AD&D, though, players both casual & serious will blithely ignore the bits they don't understand, have the DM handle the complex bits, or house-rule them. My high-school group did all three of those.
- D&D also has a long history with prior editions—including the oft-maligned 4E that drove so many to Pathfinder (itself a version of D&D)—so people who have fond memories of playing those editions are motivated to play 5E, even if they don't like parts of it. And the odds are, just because 5E does many things differently from prior editions, there are some parts they won't like (whether they are designed well or poorly). They too can house-rule the parts they don't like, or if they can't stand 5E as a package, they play some other edition, or some other game. (Or complain endlessly on forums about the parts they don't like, in narrow or broad brush strokes. ;-) )
5E definitely has design problems;
any design has problems. 5E definitely has design
decisions, at many levels, that people do not like in spite of liking the game overall. Some are changeable with house rules. Some are so intertwined with other subsystems or elements that chaging them with house rules would be a huge amount of work (but not impossible).
The survey question was "Is D&D combat fun?". In the end, fun is a subjective opinion, so it doesn't make much sense to argue someone is wrong for not finding something fun, or for explaining why they don't find something fun or what would make it fun for them.