1) Your argument for Del Potro is the same than for Tsonga, therefore you admit that Del Potro isn't a a better player than Ferrer on clay
2) Tsonga is a clown on clay and absolutely no a threat. Djokovic was playing garbage and should have lost to Seppi, who was as close to win as Tsonga was. Ferrer would have beaten Djokovic.
1) No. Del Potro is a better player on clay in general, Tsonga is simply the bigger threat.
2) Did you watch that match? It was arguably the best Slam match of the year, Ferrer wouldn't even have taken a set because unlike Tsonga he doesn't have the firepower to trouble Djokovic at all. And by the way, Seppi wasn't close to beating Nole at all, he won 2 sets but was never close to winning a third, Tsonga actually had multiple match points.
You really are out of control. Let's see: the last time Djokovic and Ferrer played it was a close 3 setter for Djokovic (in his career best season) and the 3 times before that Djokovic LOST.
Only one other player has a better record against Novak on clay and that isn't Del Potro by the way.
Ever since Djokovic became the dominant player in tennis, Ferrer has become like an annoying mosquito that he swats aside with ease. The only exception to this is WTF 2011, where Djokovic was burnt out after one of the best seasons in the Open Era and countless wars of attrition against Nadal.