I have to congratulate the OP here. There are not many quality threads in GM but this one almost manages it
Yes, but that doesn't explain why Simon should give Federer trouble when another 'grinder' - Ferrer - who also doesn't give away free points, also is rock solid from the baseline, and also feeds off pace is absolutely owned by Federer...?
IMO: Ferrer hits harder than Simon so Federer can use his pace from the baseline better than he can with Simon. Against Simon Fed has to make the pace himself which is more difficult for him.
Simon also has a better defense and passing shots than Ferrer so that makes him more dangerous for Fed e.g. when Fed tries to attack.