For perspective, look at some altcoin trading engines like poloniex. Swarmed with bots these engines express no considerable lag at all, neither do the web frontends.
Even if the engine has unfixable throughput problems, this could be tackled at the incoming end: new orders should be denied by API/web frontend if they can't be executed in a timely manner. Everything else is borderline criminal.
See my thread regarding Poloniex lag and not being able to trade at crucial moments:
https://bitcointalk.org/index.php?topic=1830920.0I wholeheartedly agree that the ethical burden is on the exchange. They can control how many trades are taking place simply by halting trading or limiting the number of traders either at one time or in general. The thing is, with all the fees these guys are making daily, it really should be no problem for them to hire top notch engineers to solve these problems for good.
My guess is they either don't want to solve the problem or are creating the problem themselves.