You have taken one aspect of German grammar out of context. The many forms (morphological? ) of German are part and parcel of the case system, which is an integral part of German - as it is of Latin, and many other languages. For learners whose native language has no case system, or (like English) only the vestigial remains of one, a case system is difficult to comprehend initially. The lack of one in a language is difficult for people who have grown up with one. Cicero, were to to be suddenly transported to modern England, would be dumbfounded by the importance of word order in modern English. . The fact that an amorous situation can be formulated in English only as 'the boy loves the girl', in German as 'der Junge liebt das Mädchen' or 'Das Mädchen liebt der Junge'; or in Latin as any of six orderings of 'puer/puellam/amat' does not make any one of these 'easier' or 'more difficult' than the others.Regarding the complexity of German compared to English, consider that the most common word in English, "the", has at least 6 variants in German (der, die, das, des, dem, den) and probably twice that many "slots" for their use -- which must be gotten right or the German sounds illiterate. Add to that that these same words function as relative pronouns. Our word "a, an" which changes only because of elision (like the pronunciation of "the") offers in German a similar challenge.
(Incidentally, many speakers of German dialects do nor 'sound' illiterate if their versions of the various forms of the definite article appear indistinguishable. They might appear to be not very well educated if they used an incorrect form in writing. There are, however, books on German usage, just as there re on English usage. Native speakers don't get it right all the time.)As far as I know, there is no evidence that English is any 'easier' or 'more difficult' than any other natural language.In many ways English is beautiful in its simplicity -- except for spelling.