No support for cryptocurrencies would be #1.
Also, I don't like Ninja's charting graphics. Looking at them strains my eyes. Sierra's are much crisper and clearer.
Chart functionality can be aggravating as well. Like zooming in or zooming out for example. This basic chart function with NT is a pain.
Additionally NT feels bloated compared to Sierra, which is so refreshingly light. I have yet to experience it slowing down for anything.
Crypto is the only real reason you listed. The rest can be adjusted. My main issue sign Sierra is their language. Ninja gives me full power of c# for my Algos. Order handling for large size is amazing. Plus great support. Ninja has too many amazing features to list here

