I think you're right. For gaming, I agree. But the sharpness is very noticeable for daily use especially since I deal with a lot of text and I love the sharp, crisp image that you get with higher pixel density displays. But as games will continue to optimize their textures for 4K contents (rather than using upscaled textures), we'll continue to see improvements even at 27-inches. I want a display that can do both very well.
That's relative though... as games optimize more for 4K, the bigger 4K screens (when they appear and with equivalent PPI) will net those rewards too, while offering a more immersive experience. And the significance of that is not to be sniffed at. Having experienced 1440p at both 16:9 and 21:9, it really is a big step up when a game takes full advantage of that extra width. I'm sure the PG27UQ is going to make a lot of people happy, but it's soon going to be at the bottom rung of an HDR 4K gaming experience as bigger screens come out. There's also a big question mark over a GPU capable of pushing it... again, by the time we have a card capable of that, we may have bigger and better monitors available.
As to your earlier point, while I certainly can appreciate the flexibility x3 monitors can provide in some situations, it's not for me personally, I'd prefer one big 40" 4K HDR 144hz screen (I can dream). Besides, you will find you are VERY MUCH in a tiny niche (with perhaps some Sheikh millionaires to keep you company) if you would be considering buying x3 £2000 monitors lol!!