You are correct that there is a 200W max in the system you mention, but that really is not much unless you are installing it in the cab of a pickup truck or only care what it sounds like inside and are not out to impress the neighbors. Trust me when I say that 135W/channel times 4 channels (540W total) doesn’t sound all that impressive ten feet away, but will deafen anybody sitting in the car possibly for a while, if not permanently.
To add on, a 300W RMS system will beat the crap out of a 500W peak system anytime, anywhere, anyhow. While peak numbers are impressive, what you really want is sustainable output unless the only thing you care about is bass thumps. In other words, the RMS number is actually more important for most setups.
Another thing to bear in mind is matching the speakers to the setup. Like @IchtheosaurusRex says, transients kill. The reason many lightbulbs burn out is the thermal stress of going from ambient temperature to operating temperature; a transient. While it’s a bit different for speakers, the fundamental theory still applies, so don’t buy speakers too big for your amp.