di quanto di or che = than. And , yes, di quanto is also how much. In Subjunctive "di quanto" is used as "than." "piu' facile di quanto" was translated as "easier than" with five examples I found. But DL will not show that phrase.
Subjunctive required here due to E' facile (also E' bene, giusto, importante, im & possibile, im & proabile, incredibile, male, meglio, ora (time), peccato (too bad), peggio and non peggio, strano)
We have struggled with the imperfect subjunctive, when it has no relation to the three past uses of the imperfect indicative: "used to (verb), was (verb -ing, and past tense of (verb) -ed. This statement from a Grammar clarifies:
the imperfect subjunctive can effectively express any tense—past, present or future—or no tense at all. Indeed the name “imperfect subjunctive” is ill-chosen because it suggests an analogy with the imperfect indicative where none exists.
Your version is formally correct, but as a native speaker I would translate it as "di quello che potresti pensare". It's hard to explain it but, without subject, there's an implicit first person ("È più facile di quanto [IO] pensassi.") In this case, in the italian version you should make the subject explicit: "È più facile di quanto TU pensassi.".
I posted this on another thread, but this confused me at first, so here's the explanation!
When comparing your expectations, i.e. comparing a state of affairs with what we thought, expected or imagined we can use one of two constructions: "di quanto" or "di quel che." This is followed by the imperfect subjunctive or the past imperfect (apparently depending on whether we are speaking formally or formally.) But it seems I'd generally go with the subjunctive following di quanto.
Il corso d'Italiano era più facile di quel che pensavo= the italian course was easier than I thought.
Il corso d'Italiano era più facile di quanto pensassi
It's been one year since I posted my original thoughts, and I can answer that now.
If you believe something or have an opinion to express, then you choose the subjunctive.
In my original post, I was treating "quanto" as a single word, where now we can see that it is part of a phrase, "di quanto".