Hmm. It seems clear that where you start from plays a role. At the same time, it seems obvious that Latin grammar (3 genders, 6 cases, 4 verb conjugations, 5 noun declensions, multiple moods etc) is more complex than Italian... or am I wrong?

It also depends on where you are going. If your goal is native fluency including clean pronunciation and grammar I find most languages equally hard. (Have mastered or had runs at 7 other than English.)

To your second point, Latin inflections are for the most part very mechanical, even for verbs. Latin is difficult to master due to the fact that it's for the most part only read. It's far easier to gain fluency if you develop an active vocabulary through speaking and writing.

If you are looking for objectively hard things to master I would pick German noun gender or Japanese Kanji. They both require rote memorization of thousands of items. Both have relatively weak patterns to cut down the amount of cases you need to memorize.

> At the same time, it seems obvious...

English: "My wife sent me an email", but "My wife sent an email to me".

Yes, very obvious :)

LOL, I got a downvote. I didn't know there is a "Party against Grammatical Cases" on HN :)

Linguists don't really believe in objectively easy or difficult spoken languages. Written language is a different thing, and the difficulty of learning Chinese characters will be a drag on international acceptance in the scientific community.