I was big on the forums up until a few months into BfA and I have always seen a trend of dissing the current expansion. Admittedly Cata, WoD and BfA always got the major flak, but after WoD there was a surge of threads focused solely on it, at least on MMOChampion, and even if other expansions' flaws were discussed, the topic would quickly divert towards WoD.
Also a sizable group on the forums hated MoP's guts because of Garrosh's personality change and, most of all, because of the pandaren.
My point is that everyone has a preference (there are people that strongly dislike Legion as well), but I did notice a trend of WoD being considered the all-time low. I am going purely by experience here though.
As for which one is worst between BfA and WoD, I would still say WoD comes out on top of the turd pile. It is true that BfA has boring content and a mostly awful and pointless story that wasted great characters, but WoD had almost no content at all and they had to come up with excuses, retcons and concessions just to make the expansion exist lore-wise.
I think Mythic+ played a big role. It is not novelty content like it was in Legion anymore and some would argue that the concept is stale, but it adds tons of replayability to content you would never visit again by just adding modifiers and tweaks.
EDIT: You are not saying outright that BfA is bad/the worst, you are comparing it to WoD. You are kind of proving my point by comparing the current expansion to the perceived all-time low