There is a good interview with Vivaldi founder on Tedium [1] where he basically says that because most browsers are built on Chromium nowadays, you have to innovate on features and that is the direction they took. And really the number of features in Vivaldi is staggering including some great ones like Tab Stacking and Tab Tiling.
But adding this many features took a toll on performance and it is about 25% slower than other Chromium based browsers. Also I assume that is the reason why is there no Vivaldi on iOS.
[1] https://tedium.co/2021/02/05/vivaldi-browser-history-profile...