The grammar rules make no sense and sometimes have more exceptions than cases it applies to.

said the native speakers of like half the languages on this planet

Dutch grammar is about as regular as most West Germanic languages (Germanic grammar tends to be relatively irregular compared to the norm though) but something that may make it less complex in many respects than languages like Icelandic or German is the total lack of cases (in the modern standard) and only 2 grammatical genders. of course, when looking at that part of the language, languages like English and especially Afrikaans are much more straightforward, with a complete lack of grammatical gender, as well as Afrikaans being very regular.

Althoughhh Dutch, and English, do have extremely opaque orthographies in terms of reading, trying to figure out the pronunciation of a word based on the spelling is pretty much useless most of the time, which isn't super common among writing systems. But that doesn't mean anything about the languages themselves.

But pretty much every language has a lot of speakers who think it's super hard and a lot of speakers who think it's super easy, when in reality no language is inherently hard or easy to learn – 99% of what makes a language easy or hard to learn for someone (other than motivation/passion/necessity/exposure of course) is how familiar it is to their native language(s) and other languages they speak. English speakers will go around saying "English is the hardest language to learn" or "English is the easiest language to learn", same with Dutch, Hungarian, Hindi, Armenian, Tamil, etc. But English will generally be one of the easier languages to learn for people who speak e.g. German, Dutch, Norwegian, French (although the spelling is a completely different matter). Hungarian and Estonian will be relatively easy to learn if you speak, say, Turkish or Finnish. Ukrainian is pretty easy to learn for Belarusian & Polish speakers, Arabic will be easy to learn for Hebrew speakers. Japanese speakers usually find Korean extremely easy, and vice versa, while both may find English extremely hard, and vice versa.

I mean learning a language well enough to use regularly at all isn't easy by the slightest measure, and it takes thousands of hours of frequent study & usage, so when I say "easy" I'm speaking relatively. I find Russian knowledge far easier to get/retain than my German skills for various reasons even though German is more similar to the languages I know the best (learning material and liking the language obviously plays a huge part in this).