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Now give me match where Nadal played without his forehand to "prove" he is as bad as you "proved" for Fed without serve at ao 09...
Maybe Nadal would have massive flat forehand and would wipe out of court everyone with his offensive...
This is too imaginary anyone to be right... Ill stick to my feeling on topic...
The OP states if the player had a top 20 shot, what you are describing here is a top five shot, at worst a top 10 shot. No top 20 shot would wipe out the court with everyone using his offense. The two things are contradictory. So, you're not quite on topic with that statement.
Basically, you are saying, a Nadal with a top 20 forehand, is going to be beating or being on equal footing with a Federer who arguably has the GOAT forehand, and unarguably the top five forehand of all time. OK, if you feel so...
In regards to finding you a match with Nadal playing with a bad forehand against Federer...strange request honestly. You do understand that Federer and Nadal will only play each other in semis and finals of events, which means you are asking me if Nadal has actually navigated through draws without his forehand to play Federer in the final....the fact he hasn't managed to do that should give you a clear indication that if Nadal cannot make it past lesser players with a weak forehand to get to Federer, what real chances would he have against Federer himself. Before you say it is all about match ups, a few things - firstly ONLY Djokovic has beaten Nadal more than Federer, meaning Federer is more superior against Nadal than the rest of the field, and secondly, without his forehand spinning up to the backhand and those incredible RPMs gone, the match up will no longer exists...and back to the first point....this topic is about a top 20 replacement shot, not a like for like replacement that you proposed in that post.
If Federer has blasted a Nadal with a decent forehand off the court enough times, then you don't really need to be a rocket scientist to understand what he would have done to a Nadal with a top 20 forehand. Federer losing his serve still doesn't take away from his ground game and return game.
Anyways, maybe we are being too imaginary here.