If you look at physically the more recent WD drives versus the equivalent / older HGST models, I would argue the newer WD, especially enterprise / helium filled models, are really HGST under the hood. The shape of the drives are clearly the same, and it's not as if WD wanted to ditch the manufacturing plants and technology when buying HGST. WD HC530 Ultrastar for example, pretty sure that's just an HGST drive for all intents and purposes.HGST is actually owned by WD now, and the drives are WDs under the hood. The other manufacturer besides WD and Seagate who makes drives themselves instead of just relabeling is Toshiba.
And yes, all of them have put out some terrible products over the years, as well as some excellent ones. Spinning rust is a fundamentally unreliable technology, so failures are to expected from any brand -- that's why we have RAID. It's valid to compare failure rates between the different manufacturers, but you really need to do that for a particular capacity point or year for it to mean much, because when a new technology is introduced (such as HAMR/MAMR), that can change the whole picture. Backblaze data is pretty useful for making those kinds of comparisons: Backblaze Hard Drive Stats
There was also a long period after the acquisition where China held up the merger because they wanted to ensure HGST drives continued to be manufactured in China, so even after the acquisition for quite some time there were two separate lines where a true technology / product line merger was not allowed to move forward.
I think for a while you'll see some WD product lines that clearly reflect WD engineering, production, and design, and some product lines that clearly reflect HGST engineering, production, and design.