Ok… let’s go with that, and then let’s review what German science tells us about the prehistory of Germania:

“Germans” lived like the much later Slavs
“Germans” were named like the much later Slavs
“Germans” had funerary rites like the much later Slavs
and now:

Germans looked like the much later Slavs*
(* note: the Germans that “looked” like Slavs are those from Poland and East Germany – as far as I know, no one has conducted similar studies in West Germany)

Combine this with the fact that there are no (zero, nada) sources suggesting any Slavic migration into Germany.

German conclusion:

Germania was occupied by Germanics only and Slavs came into Germania much later.
Notwithstanding, Tacitus and many other eyewitness accounts she implies that the Germanic population was diverse, almost multiethnic… Of course, Tacitus did differentiate the Suevi from other Germans but that could not have been Slavs we are told. In fact, she seems to think Germania was home to every type of person (but seemingly didn’t include Slavs… except maybe their biological ancestors… say, what?).