I believe it will it’s going to have modding support
BG3 is a different type of game. You dont grind for loot in BG universe - you play for the RPG part. While games like diablo is for the A part (action).
I played BG3 in early access and refounded it, it was that bad (prefer Pillars of eternity etc) - but after the latest changes i WILL play it again (for the story). But i will also play diablo 
Here is the difference. When POE came out, it tried to sort of fill the gap that was left by D2 being too old by then and D3 being at least initially trash. POE was made by a small at the time company with no history and no built-in fanbase. For such an endeavor, it succeeded, but it was not amazingly polished and frankly was at least at first confusing to many. Also, it’s graphics were a solid meh.
Now, they will be coming in with a large budget, a loyal fanbase, many of whom were former Diablo players and most importantly, on the skirt tails of a very dissapointing (at least as of now) Diablo 4 game. They will be able to re-grab both their own fanbase and a large chunk of the Diablo fanbase due to those factors. They no longer have a problem of ppl not being sure about them, because they proved they can come up with a very solid product. OTOH, the Diablo team has now proven that they sadly, cannot. See, POE1 had to prove that they can, and did. Diablo 4 team, after Diablo 3 and the success of POE had to prove that they are still kings of this genre and they failed and after this patch - failed miserably.
Just so you understand that I’m not a POE fanboy, I did play it during beta and then a few years ago for a month or two. I liked it but was not in love with it. I have no stake in them succeeding. I wanted D4 to succeed. They succeeded at being highly profitable, certainly initially, but sadly not at being a good game.
Apples to oranges… apples to oranges.
It will definitely take away players because Diablo 4 is looking too weak to compete with even older games that I and others have gone back to. Pre-season patch was basically them promising an ice cold lemonade and serving up a glass of straight vinegar. Yuck!
I mean, Baldur’s Gate 3 in an infinitely better game made by an infinitely better studio that actually cares about their players and listens to them. D4 just wants our money. Of course BG3 will be better. You’re comparing a Lamborghini to a wagon full of dog s#it.
stardew valley will kill everquest