This is just my personal perspective:
I started as someone who started a World of Tanks thread in here, played the heck out of it or 3 years, spent $200 on it to acquire premium tanks and free XP, unlocked nearly all the tanks that I wanted (until British tree was released), and I believe I ended up with more than 10,000 battles (and another 2,000 in closed beta).
Nonetheless, I still decided to do fully transition to War Thunder because of both technical superiority of the engine and better customer service. I was heavily invested into WoT but the more I hung on to it, the more I'd have to cope with the losses in time and financials.
I do miss WoT, I actually made friends in that game that I'd see in real life. But hey now we have Bay 12ers playing War Thunder too and don't have to deal with the server clustering crap that made me lose some of my Oceanic mates in WoT.
The problem with WoT is how grindy it is. There's only vertical sense of progression. A lower tier vehicle has little chance against a higher tier vehicle, except in rare circumstances (e.g. capping contest between a scout and a slow heavy, assuming both are at equidistant to each respective cap point).
The engine is very resource-intensive compared to War Thunder. I was able to run War Thunder beta better than I could WoT (release version, a couple of years after beta). The visibility mechanics and shells disappearing at certain distance are absolute bollocks and are designed as a way to camouflage (see what I did there?) the small map sizes. They can't design larger sized maps because, well, it will hurt performance too much on low to mid end rigs.
Anyway, I'll stop here. I've come a looooong way to realise that War Thunder is what the future holds for me. Looking forward to flying and tanking with you all.