I understand your point, but I think VC backed companies are likely in a more hyper growth mindset than banks and conservative industries were when they were making these systems in the 80’s.
As much flak as I’ll get for saying this, why Python? It seems like Robinhood went all in on an ecosystem that is easy to get an MVP off of the ground with, but certainly not as fast and reliable as you would expect a system moving billions everyday. Language typically doesn’t matter for end users, but man, there are at least 10 solid options to build a critical trading system in that are faster and safer than Python.