And wow, guess what? Germanic languages most resemble your mother tongue, since English is a Germanic language. It has large portions derived from Latin and French, so Romance languages being second place isn't surprising, and as you note, same script. The more different things get from English, especially in script and spelling, the harder it is for you to learn. Maori, like its cousin Hawaiian, is well-known for keeping a short and sweet orthography (only fifteen letters, of which five are vowels that can come in long and short form, and for Maori, two of the letters are digraphs, ng and wh)...and because Maori did not have its own script at the time Europeans came and occupied the islands, the Roman alphabet was used for the task. Again, similarity to your mother tongue is what makes it simple, far more than anything inherent to the language itself.
Now, look at world languages overall. Mandarin Chinese is the native language of twice as many people as English. 7 of the top 10 native languages by population do not use the Roman alphabet (Mandarin Chinese, Hindi/Urdu, Bengali, Russian, Japanese, Yue Chinese, Vietnamese.) Of these, many do not use the grammar English does. Some are tonal and most are not stressed like English. Many don't conjugate verbs at all (that property is handled by context, or grammatical particles, or some other structure). Most have cases so word order isn't nearly as fixed as English, and things like articles are unnecessary in many contexts. Etc.
All of which simply furthers my original point. If you're deeply immersed in D&D and have vastly more experience with it than anything else, your "mother game" as it were, then sure D&D is going to be easier to learn than other systems, you already know most of what there is to learn. If you're actually new to the hobby, which most 5e players are, that's not going to be the case.
We should be looking at this from the perspective of folks who speak Chinese trying to learn English, not the perspective of English speakers thinking about how easily they learned English the first time...