There is a difference between 100 and 200 tabs, plus which Vivaldi version are you on? Builds up to 3.6.2160.3 work fine with ~400 tabs, and by fine I mean ~1 second Tab switching. Instant is very subjective. You will probably also call going fullscreen on YT instant, yet here it is measured https://www.youtube.com/watch?v=-uCA2qIIG1M