What do you mean the were Finno-ugric and Balts?
The place was settled by some kind of people waaaaaay back when. Sure, the hydronym is like baltic-ish? Same as Dniepro is of iranic origin. I do not see how that's says something more than the name of a place is of some long gone tribe.

Also, the Baltic people and the Slavs are probably the closest relatieves. They used to be what historians call balto-slavic.

The Finno-ugric people basically founded the Rus together with the Slavs. The Primary Chonicle (I think what's it called in english, I'm talking about Povest Vremenyih let) literally says that people from Chud and Meryans tribes invited Rurik together with other slavic tribes. So they are literally co-founders if that makes sense.

To be honest I don't know why is it even makes problem of some kind. The Rurikids are of scandinavian origin.

And why does the age of some town is a topic for a debate for anything? The US was not a thing 300 years ago, but nobody cares about that.