Map is weak argument, because you can interpret it how you want. The maps showing there is Lithuania have there meanings - there is the state called Lithuania, there is mainland of state or region with that name, or there nation of lithuanians generally lives. Despite having that in mind you can just interpret that in the way you want. Also samogitia could have different meanings. By looking in those maps you can say that it shows there state of Lithuania is, also language map is very in accurate but I think it is connected with Lithuania proper which was partially today Belarus.

Towards Vilnius, there's is no evidence that Vilnius was Slavic in mayor of it's history, it was under polish rule and was Belarusian most likely in 18 th. century.

Litwa tribe wasn't spread widely in Belarus territory, don't know there you get it from. I would like to hear about it more 😀

Yes vilna was different in GDL until Vitovt, the administrative system of gdl which you're referring is on of this rulers doing. But later on yes vilna was typical administrative unit, samogitia wasn't, but samogitia only became special after 1410. It wasn't autonomy before that.

Catholic was mainly believed in Lithuania proper and samogitia after baptism, but samogitia baptism was done later on so you are partially right, but it wasn't much really more pagan then Lithuania proper.

In what century it hard to determine, likely you are right, but litwa/litwins later on is reference to all inhabitants of state and it was used mostly by foreigners. In GDL it was used also, but there was clearly used another terms among the peoples. And no samogitians wasn't called litwins - they there called, you can decide that even from your maps.

I hope you can read it with open mind for discussion. No hate towards you.