7 Pro user here, I also don't have VoWiFi, but it's not really a dealbreaker for me since regular calls work just fine. I can also borrow a family member's S9 if it really came down to that. I've heard OnePlus is notorious for having issues getting VoWiFi to work in their Indian market, so it's not just Visible having this issue I suppose.
Otherwise, my experience with my 7 Pro has been with very few, minor hitches. It's the first phone I bought with my own money and I feel it's one of the best decisions I've made on a phone. Hoping it lasts for years to come!
I enjoy my phone... I just wish it was better at switching between LTE towers at times. Sometimes it will lose reception in an area with amazing reception and not reconnect until you toggle airplane mode... But OnePlus also has this issue with other Verizon based carriers.
The official list days the OnePlus 8 and 8 Pro support WiFi calling, but my device has no options for it, and wifi calling provisioned isnt checked in the 4636 phone debugging menu.
I used the OnePlus 7 Pro for several months - that device was great. Great quality camera and snappy processor for the price. The OnePlus 8 is more expensive with less impressive camera and other specs. OnePlus also has a much smaller choice of cases than others. I specifically use a case that can hold my drivers license and a debit card, and there was no such case to be found on Amazon. It's not in the class of a Samsung GS21 Pro that I use now (not even the Ultra, just the Pro). And yes, no wifi calling.