>>17852688German and Icelandic are the only Germanic languages retaining a case and full gender system and even then they're quite simplified in a lot of ways. German dialects go a lot further, some have no gender, all lack the genitive, some even have do-support. So all these things clearly have a tendency to emerge naturally and don't require foreign influence as an explanation, much less creolisation.
Uralic case systems are weird, Uralic languages sometimes gain more cases than they had before as well which is extremely unusual in IE which has a strong tendency to only become more analytic over time.