It depends what you mean by easy. Even if you are using a slow chain, you still have to compete for finite block space, you still have to work out how to risk/matching fast, etc.
With chains built for exchange use, operating them easier, that is why they don't require thousands of engineers. But the actual technical capability of the system is significantly in excess of tradfi exchanges. For example, risk function is real-time on-chain as opposed to EoD settlement. This significantly changes the possible feature set. Once you have built it, it is very easy...the question is why big exchanges rely so heavily on eod processes? The answer is: they are bad at engineering.