1: Very good to good
Lahm, Azpelicueta, Carvajal
2: Good
Walker, Alves, Alba, Marcelo, Hakimi
3: Poor
Cancelo, Alexander Arnold
It's not concrete of course as I may be over or under generous with some in the 1 or 2 range. The actual category isn't that important for me but the 3 tier distinctions.
From what little I've seen, Frimpong may be somewhere in between 2 and 3 as a RB/wing back. If he's a '3', that's really bad and if he's a '2' then that's more than fine but either way the team he'll play for will have to accommodate his lack of height and his very attacking nature. So whilst it's true we can offset this with his other qualities, I think if they fall below the 2 or at the 3 mark, then you'd got to be very careful about the set up.
I wouldn't really lump Lahm, Azpelicueta, Walker and then say 'well yeah all other full backs are around that kind of defensive range and they work for their teams, so Frimpong can be easily managed too' if he's closer to the 3 range. It could be an Alexander Arnold situation at Liverpool, except they're been much more successful and organised than a team like ours. So rather than being a good fix or solution, it could be a side-step issue and create unbalance.