Its counter intuitive but a certain amount of irregularity helps languages. By far the easiest rated languages are isolating and lightly inflecting langauges, and from my experience this is even true if your native language is agglutinative. What a lot of these "easy" languages have in common is that theyre not inherently regular, they have irregular word endings and totally arbritary ways of constructing sentences in a way to convey meaning. On the other hand you have of course the languages that are just so irregular that theres no vibe you can go off of like in romance languages(theyre extremely easy to learn if you move to place where theyre spoken) like navajo. Many words go from "i mean that "s" or "a" fits there" to "why is the word form changing completely in this one specific case", on other words you loose all grounding. But i believe the reason a lot of people struggle with highly synthetic languages is the exact opposite, you have to specify everything in the right way or your sentence wont make sense. In highly irregular languages any piece of a sentence could be very important to the meaning, in a highly regular language every piece of the sentence is important to the meaning and right in the middle are languages that mostly follow rules but not always. Also in very regular languages its often not possible to make the reductions which humans love to do. You might have to specify a piece of information over and over in different ways without it leading to the sentence being more understandable. Idk these are my two cents as a definitely native speaker of hungarian and kinda sorta native english speaker.