Mykolenko is inconsistent, however I'd refute that he isn't PL quality. Is he at the lower end of the spectrum? Yes, but it is what it is.
The lack of cover is the issue, where I think Godfrey's versatility did a job. The right back situation is worrying too, with Coleman needing replacing.
In terms of defence, Tarks, Branwaithe and O'Brien should be enough if you then factor in Keane as a cautious backup* - it's far from a terrible defence.
But we can go through all the positions... the depth is a worry, like I said. The deeper issue, nevertheless, is how you utilise the squad and make decisions.
Is the squad great? No. Is the most being made of the squad? Equally, no.
*Again, Godfrey's versatility will be missed.