I used to work at the big investment banks for a long time. Around 2015 they began transitioning their native apps to web apps (mostly for high-touch trading),

I used to work at the big investment banks for a long time. Around 2015 they began transitioning their native apps to web apps (mostly for high-touch trading), so VM based languages are very much used for initiating trades to various degrees, of course in the majority of the cases the actual FIX message gets created in some back-end running C++ or Java. But there are exceptions, FIXParser was used to create the actual, real, over-the-wire FIX message to trade a trillion dollars in a couple of minutes by a large financial institution. And this is just one example I heard directly from the people involved. The library does not have any metrics/analytics so I can't actually know how much it's been used in the industry.