Not to mention that MOSS is the 'simplified' way... if you don't comply you would actually have to register and file VAT in all countries separately.

Yes, this is a good pointer. However, there are likely more problems than just VAT MOSS — for example, it is likely that your home country will want you to charge VAT to your customers in the same country, while using VAT MOSS or reverse charge with customers in other EU countries. The result is that your subscription plan pricing gets significantly more complex.

Some countries also have requirements as to invoice language, or conversion rates that you need to use for foreign currencies. In my case (Poland), I can use the European Central Bank (ECB) rates for VAT, but not for income tax further down the line, so I have to integrated with two central banks to get their rates.

Overall, there is lots of overhead. There is a disconnect between EU officials and small modern companies. Officials want to "promote innovation and entrepreneurship" while introducing heavy-handed legislation (really meant to hurt Amazon, in case of VAT MOSS).