I'm pretty worried about this, too. I played PoE1 on an i7 4790k, Fury X, 16gb DDR3 and it was hovering around 20-30 fps throughout most of Defiance Bay and any fight with more than a couple wizards casting at the same time.
Also, towards the end of the game, loading screens and menu-ing were unbearably slow.
I was really hoping they had made performance a priority after all the feedback they got about the first game, but the streams I've been watching this past weekend dashed those hopes.
I don't know anything about game development, but I do know Unity engine games almost always have poor performance from my experience, I wonder if it would have been viable to spend some of the backer money on licencing a superior engine? I assume it wouldn't be an easy task changing engine, but it definitely would have been good for the game IMO. State of Decay 2 has moved from CryEngine 3 to Unreal Engine 5 so I guess it's possible.
It's been a long time and I'm sure Obsidian is made of very different people now, but they have just never been good with engines. If these are the same people who were working on Fallout 2, Icewind Dale, Neverwinter Nights 2, KotOR 2, Fallout New Vegas, Alpha Protocol etc., then I think it's about time they should consider investing in some talent that can improve and optimize the engines they use.
I'm seeing this pattern where they are only able to achieve good performance when they use an already developed and optimized engine for a sequel or very similar game (Icewind Dale, Fallout 2, NWN2, KotOR2). With Pillars, Tyranny, and Alpha Protocol, they licensed Unreal and Unity and did all the work themselves. Those games turned out with very poor performance.
Of course, I'm not a developer and I have no idea if any of this makes sense. It's just a pattern I noticed. I love Obsidian's games (almost unconditionally at this point), but engine-related things seem to be quite a weakness for them. And with all the success they've been having lately, I was really hoping they would make a point to address this common complaint for Deadfire.