A lot of older people in Germany got their first email address with gmx or web.de (same servers, just different domains), so both of these platforms users are often targeted by spammers and scammers because of a possibly higher success rate. My FIL just last week almost lost control of his gmx and associated accounts. Though that was probably due to using the same password for multiple services, it is just more likely to happen with gmx than say posteo due to probabilities.
Spam also comes from the providers themselves, trying to push subscriptions to their premium services. If you want to access your inbox via browser and have an adblocker enabled you are forced to watch an ad.
If it works for you and if you use a separate password for gmx (or better yet, a password manager) and a different client, all good. I just think there are better options for people who are looking for alternatives right now.
I can recommend Asphalte from France. https://www.asphalte.com/ Gotta bring some patience when ordering though. They collect orders and only produce those with a small overhead to cover returns, to avoid overproduction. Their style focuses on timeless stuff in good quality as to avoid trends. You can’t always order all their products, but some ‘eternals’ are always available to order (still have to wait until the next production cycle though). Now would be a good time to order summer clothing. My personal favorite are their sneakers as they look good and are very comfy and sturdy.