Trying to grade an OL is very difficult in most aspects...
however, it is possible to watch an individual's performance and just judge the intensity, athleticism, movement skills, etc vs 1-on-1 defender.
Since we don't know the block assignments and the way the coach wants them to play...we CAN watch and judge
how they engaged and the way they look when they block - kinda judging movement/athleticism, violence, strength, etc...I think that is fair to observe and form opinions on their style of play. Did the player they were blocking make the play? Did the player push them back, etc...stuff like that. NOT on the whole outcome of the play...just their small part....and even then, it's not the whole picture but there is info to be gleaned there. imo
"L'audace, l'audace. Toujours l'audace!"