Well, I say it’s not about the front end or back end… Here’s how it goes. Every team requires an Architect or a suitable candidate who plays an architect role.
Front end developers are generally good in front end, that’s where they are specialized. Back end developers are good in developing API’s, Web Apps, Database design etc. However it all depends on the projects where some requires a dedicated database developers and DBA. But the back end developer should be able to handle all to some extent.
A full stack developer is good in over all end to end. However we cannot expect a full stack developer to be a GOD of software. For sure, she/he is not perfect like the font end or the back end developers. Considering a full stack developer is always good for a small team. However i would say, it depends on clients and project requirements. Some projects require a special skillset like building an AI based product. Where a full stack dev can do but she/he is not an expert either.
Coming to experience. Any where b/w 0-3 is considered as Software Engineers and they are not the senior ones. Let’s say going with 5, they are the senior folks. There’s a catch, a developer simply sitting and working on something for 10 yrs, may or may not give a value. Years of experience does matter but it depends on folks what they did. How complex projects one handled in the past etc. An experience is experience something needs be practiced and done well. We cannot buy something in the market :)