I'm not sure if the Gainwell or Penny "best\worst" assessments are valid overall. Gainwell's PFF Pass Blocking - HB rating'has been getting better during his 3 year career -- from Poor to Below Avg his first two years to Good so far this season. These are inherently SSS (especially thru 5 games this year) and with wide difficulty variation. So definate improvement, but I definately wouldn't consider him one of the best blitz blockers in football.
For instance, Penny has had only 2 PB opps this year and I believe one was a free runner up the middle blitz where he got blown up by the blitzer v\ Minn. Compare that to having to seal a DT where the OG had the DT largely contained. Large differences in difficulty. So with only 2 opps Penny is rated Poor this year (but excluded from overall rankings because of SSS).
But career wise Penny has had 2 Good, 2 Avg and 1 BA rankings overall in his prior 5 pre-Phil years. I would tend to trust his PB overall vs Gainwell's.
That said, even with Swift, being rated Avg is based on 17 PB engagements in '22 and 20 in '21. Being rated above average vs poor is maybe 2 plays -- with difficulty variations.
If I had a take away from their rankings - the best Pass Blocking HBs tend to be the more robust\physical HBs. If you look at a 3 year Top Ten ranking you get names like Saquon, James Connor, Tony Pollard, Samaje Perrine, Gus Edwards, Derrick Henry etc. Doesn't mean a smaller guy can't be in there (Devin Singletary is), but I think you are challanging nature if you rely on scat-backs against free runners, unless they've demonstarted a particular skill over several years.