It seems plausible they just didn't care enough and the fix actually was easy. After this long of it being slow, I don't understand why it would coincidentally happen now other than a complacent blindspot being awoken.

I updated my client and startup still takes 15 seconds. Granted, my boot drive is a SATA3 Samsung 850 EVO, but 15 seconds is still much slower than any other program I have, even Adobe programs. So I don't know if the update works universally for everyone or something went wrong.