Opera startup time may be a deciding factor on desktop PC when you need to open and close browser frequently.
I, as a programmer need to do it very often: for testing my web applications, for referring documentation and so on.
It takes me a couple of seconds to start up Opera each time. Recently I switched to Chrome and it's way faster.
I mean - it's a huge waste of time having to wait those couple of seconds over and over again during the working day.
So the feature is important - for me such slow startup may be a deal breaker for a browser.
So no - Opera start is not fast enough for some usage scenarios. Chrome is. Vivaldi is.
We need this option. Opera uses Chromium code base. So the option seems to be already there, just probably pointlessly disabled.