The Xperia 10 Plus is going to have a tough time on the free market. The Galaxy A9 (2018), for example, has dropped in price significantly since launch and now goes for less than the Xperia. The A9 is hard to recommend for its image quality but does have an ultra wide camera in addition to the regular and tele, plus a superior display, better battery life, more powerful chipset and more RAM. The Xperia has an extra-tall display to counter all that, plus Android Pie out of the box, while the A9's Pie is coming who knows when.
The Moto G7 Plus, on the other hand, does have Pie, and a similar vanilla version of it to the Xperia's. It's got the same chipset and a display that performs on par with the one on the 10 Plus - so mostly similarities then. Well, the Xperia outlasts the Moto in most battery disciplines, but the G7 Plus has an altogether superior camera output, front and back, stills and video. And the best bit - the Moto is about a quarter cheaper.
Even more affordable is the Nokia 7 Plus - one of our favorite midrangers, regardless of the fact that it's a year old. Even so, it's got the more powerful Snapdragon 660 inside, longer battery life and a fast charger in the box, plus it's more premium-ly built than the Xperia. By now it's gotten the Pie update too, being an Android one device and all, so the Xperia doesn't have an edge on this either. The 10 Plus's display is brighter than the Nokia's so there's that, but the 7 Plus's photo and video quality is a notch up.
If, on the other hand, you're willing to spend a bit more, it's worth looking at the Xiaomi Mi 9 - it'll set you back to the tune of 20% more in Europe, but likely less so in Asia, where the Mi may even end up cheaper. The Mi 9 is a proper flagship with a Snapdragon 855 inside, the camera trifecta on the back, superior display, longer battery life... There's little in the Xperia's favor in this battle.
We understand the rationale behind a 21:9 screen - the narrower body should be easier to reach across, while the elongated aspect still allows for a lot to be shown in one screen - especially for vertically scrolling apps. And it really works - once you've gotten used to the dimensions, you come to appreciate the benefits and look away when a legacy app refuses to stretch to the full height. But aside from the novel display aspect ratio, the Xperia 10 Plus doesn't stand out in any particular way.
The Xperia 10 Plus is not a bad phone, anything but. It's just that there's more than one better option at the same price point, and also a lot of phones that are just as good if not better, and more affordable. It's tough to recommend at its launch price unless you're hell-bent on having one of the first 21:9 displays, be it for productivity or procrastination. Outside of this tight demographic, we don't see much appeal for the Xperia 10 Plus.