His English is much worse than Mr Trzaskowski`s.
Pawian, a lesson in comparatives and superlatives is in order for you. Tut, tut. What
doyou teach your students? In English, something can only be worse than something which is bad.
Mary's Polish is bad but Ann's Polish is worse.
John's Polish is good but Paul's Polish is not as good.
Trzaskowski's English is actually good. Therefore the other geezer's English 'is not as good as'. If you want an equivalent of 'much worse' you would have to say 'nothing as good as' or 'nowhere near as good as'.
Now you say something a bit smart-arsey but in reality you will stow this piece of information away with all the other little treasures of English that I have gifted you :)