Is managing risk from a single trading platform a feasible undertaking considering the complexity and variety of financial instruments being traded by buy-side firms?

Yes, but the key to risk measurement (and therefore risk management) is data. What you actually do with that data in terms of risk calculation is meaningless unless that data is reliable.

So this is a prime example of junk in junk out?

It is, but to put a bit of flesh on that, it's more about getting to the point where you have a