Not really, it's use and fork an FOSS, the webstandard is a response of the most used system to access it, which is Chromium (Blink), it really benefits only the webmasters because this standard. Both other engines only can try to emulate this differences. The real problem is that since more than 20 years there isn't any new engine apart Blink, Gecko and WebKit + some few exotic forks of these (Goanna, Qt...), not really usefull for modern Browsers. The engine is by far the most complex part of an browser and to develope a new engine is a work for a lot of devs for years. There are some attempts (eg. Ladybird) where we maybe can see an stable release in two - three years, if they don't abandon it before like some others.

Even the maintance of the engine is a lot of work, not really affordable for single devs, needed to permanently check for security holes which permanently ocurres due new malware in the network (thousends every day, specially now in the current world situation) and release corresponding patches. Vivaldi is always 2 Chromium versions behind (except security patches), because the need to gut the Chromium engine and modify it for 6 different OS (Windows, Linux, Mac, Androud, Android Auto, iOS) before the new release. Hard work for this small cooperative in Norway.

A small part of Vivaldi, related to the unique UI, is proprietary, source available, not closed source. So Chrome and EDGE can't use it legally. Gecko browser have it easier to release as FOSS, there are no big corporations which use it.

https://github.com/ric2b/Vivaldi-browser