That number only sounds crazy wrong because you've done the content actively, as such the wall has never grown so large (or at least I feel is a general safe assumption for must people posting here). It is relatively accurate number assuming you're not ESC ESC ESC ESC ESC, STOP, SKIP, ESC, and are new / not know what you're doing. Like any of us who replay the game would be drastically faster just because of the foreknowledge.
400 isn't that aggressive of a number. Many people say around 70-120 hours for ARR alone, given a first time play through (I'm not talking about people who already know what to do), then you can add about 50 hours per expansion after that. 50 being a relatively fair number, as for some people they've also said ~60-70 for some expansions.
Therefore you have 3.0, 4.0, 5.0, 6.0 which makes 200 hours and the ARR making it anywhere between 270 to 320 hours. We're discussing 7.0, and so I say 400 (adding another 50 at least, and not wanting to make it sound like exact math) because in the context of this thread the assumption is either we start at 7.0 and hence it's a really fast start of like 10 or less hours to get into content or 7.0 is NOT where the fast start is and therefore you're telling people roughly 400 hours to get to end game.
Keeping in mind we're also discussing averages. Personally I 100% witcher at around 125 hours, but then I see the average is like 150+.. so /shrug. Another note to keep in mind is that is not 100%'ing everything either, if someone gets distracted, as they should (golden saucer, triple triad, crafting, gathering, different jobs, optional dungeons/fights, etc), with content as they go along, it can obviously impact the play time. 400 is suddenly a fairly fair calculation, imo (some people will be much faster, naturally, some will be much slower - we've to aim somewhere above speed runners / rushing and below people that leave no stone unturned and no quest unchecked). Occasionally I do reference further than 7.0 (like when I said 550).
As for the solution... chef kiss. Reminds me of when I told my wife I was almost done with Death Stranding and just a wait a bit before we watch a show before bed. Suddenly out of no where a, what feels like, 2 hour cutscene appears... that plan got yeeted.
Besides lets say 400 was too much to finish 7.0 and join people in the 7.x+ patch experience (or 8.0 for that matter), we want to be far more conservative. 50 for ARR, 30 for each expansion. Still looking at 200 hours (50 + 3.0 (80), 4.0 (110), 5.0 (140), 6.0 (170), 7.0 (200)). You're asking for someone to 'perfect' a game like witcher 3 - 100% no stone unturned, at a slowish pace, in order to do any new content. It's still HUGE. Though I think using 50 and 30's is far too aggressive for averaging as new players who aren't skipping like crazy and not knowing where to go are not going to be super effective with their time, while also being distracted with other side content (like new jobs). Therefore I'd call that a hyper conservative estimate, and some where around 350 - 400 more like the average person (not the average account, because the average account includes players who own multiple accounts).
So back to your point, exactly 8 hours a day for two months. Holy cow, amirite? Even if we used the, what I think is highly inaccurate, lowball 200.. that's still an entire month of 8 hours a day (25 days). So.. exactly my point. It's not horrible that stuff exists, for many that's AWESOME NEWs. But for others that's going to be like "NOPE! HOLY NOPE!" and for those of us who are playing the game actively the appearance of that wall has never really matured and so I think many are coming at this with a skewed perspective (imo, since the wall never developed all the way for them). We've eaten away at the task overtime in enjoyable bite sizes like a slow and steady tortoise, the rabbit is going to get rofl stomped by the force of it however. Also I should add that the 8 hours a day example, which I like, and I don't think you meant this either, isn't the goal for people to complete the game in lol - people should be able to play at a far more relaxing pace (unless that is your relaxing and time available pace... in which case.. good for you..). For example I have about 2-4 hours a week to easily spare so it would take me nearly a third of the year to just generally catch up in the MSQ, if I was new,... that's not even doing other things lol.