"Can I not write plausible claims?"

You certainly can write plausible claims.

The key is how you present them.

There is a spectrum:

Established fact

Strongly supported interpretation

Plausible hypothesis

The problem arises only if a plausible hypothesis is presented as an established fact without making clear that it is an interpretation.

For example:

It is plausible that...

This may suggest...

One possible explanation is...

The alignment of these developments raises the possibility that...

These formulations signal to readers that you are advancing an interpretation rather than reporting a universally accepted historical conclusion.