Of course it's about right of way. Following ROW is how we make ourselves predictable to other pilots, and how we anticipate their actions to avoid collisions.
There is nothing inherently dangerous about a straight in approach, which is why it is legal. But if you want to do so at a busy airfield, you need to understand that you are behaving differently from what other pilots expect. That means you should take additional measures to inform traffic of your intentions, watch out for aircraft who miss your calls, and always be prepared for exactly this situation. To me that means execute a stabilized descent from pattern altitude at approach speed in landing configuration, with a sharp eye on the base leg.
Blame is necessary. That is how we identify proximate cause, which helps us learn and avoid future incidents. While we can learn from the actions of both pilots, clearly the main lesson here is that a Leroy Jenkins arrival at a busy training airfield is dangerous. The twin pilot might be a nice guy and a skilled pilot, but he acted stupidly and got people killed. So don't be Leroy Jenkins.