"less plausible" is correct and can be used in written English. For example, you could say, "The theory that aliens created the pyramids seems less plausible now that archaeologists have found evidence of human construction methods."
Here, it's less plausible.
Which are less plausible?
That seems less plausible.
Ball is an even less plausible revolutionary.
And that's just a lot less plausible.
It's the reverse that seems less plausible.
For emerging markets, however, this option is far less plausible.
He is one of James's less plausible inventions.
But some of her examples are less plausible than others.
His claim to theoretical consistency is less plausible.
Other bits of substantiation are even less plausible.
Since I tried Ludwig back in 2017, I have been constantly using it in both editing and translation. Ever since, I suggest it to my translators at ProSciEditing.
Justyna Jupowicz-Kozak
CEO of Professional Science Editing for Scientists @ prosciediting.com