I really heard "trYdniejsze" instead of "trudniejsze" like the officer Crabtree in Allo, allo tv series :)
What about 'this is more difficult' ?
It's just "To jest trudniejsze", without the 'dużo' part.
Let's say that in your translation this is 10% more difficult, and in our sentence it's 60% more difficult ;)
Why can't I say ''bardzo'' ?
It would mean "This is very harder", so it does not make sense as it does not in English. Instead you can say "To jest bardzo trudne" - "this is very hard", but it doesn't mean the same.
Makes sense, thank you !