People don't have infinite time, so yes. Or you poll your knowledges together or you try to learn a lot of different thing

Everyone will have any combination of different levels of knowledge for several subjects

What's important is people invest in what they really want to do

I am a back-end developer, can I also do front-end? Sure, but I don't want to. I prefer to invest time in database and data warehouse and dabble in ML. And yet I can still only be a jack of all trades for data and back-end only. But there is no way I'll have time to do everything well and fast

Sometime ago we implemented OAuth, we did not had any experience but after quite a while everything was done. If we had someone with experience it would have been done faster, if we had an expert he would have told us that we actually didn't needed OAuth and all the time invested was a wasted