We do have a non insignificant amount of ancient frescoes, mosaics and even a handful of paintings. As the author has pointed out they generally seem much more appealing to modern aesthetic sensibilities. That seems like reasonably strong evidence than whatever thought processing went into making these so called. "reconstructions".
> To me TFA reads mostly as "this reconstruction looks bad, I refuse to believe ancient Romans painted statues like this, therefore it must be an incorrect reconstruction."
Which I agree is not a reasonably view IF we had no other data. Imposing the garrish 5-yeard old colouring book style is no less biased.
> Imposing the garrish 5-yeard old colouring book style is no less biased.
I don't think they claim this is what the statues actually looked. In fact, the article quotes an expert saying the opposite: "we can never know what they looked like".
These are conservative but incomplete "this is the part we have strong evidence for".