80% buy-in from beta participation seems like a bit of a stretch. Especially if you really did mean "additional" (as in, 2 million new preorders on top of whatever they had prior to the beta).
Personally I got multiple characters to 25 and spent a stupid amount of time playing sorc the first weekend. Had little to no desire to check out necro on week 2 so I didn't load the game up at all besides checking a couple things out with 32GB of RAM installed. It's a decent enough game and I liked it more than I expected to, but now that it seems pretty likely that courts are going to tell Sony to go fuck themselves and let the MS/Activision deal happen I will just wait for it to show up on Game Pass. (For reference it took less than a week for Bethesda's catalog to show up when MS bought them out.)
Still have massive concerns about endgame mostly being "nightmare" versions of dungeons that were extremely shitty the first time through, however.