Surely injury can't make something not-perfect in a contact sport? If the aim is to not hurt people and you hurt someone, then it would be imperfect. But if the aim is to say, take a mark without fumbling the ball, and in the process someone's injured in the contest, that mark doesn't become any less good.
I don't see how a tackle becomes more or less perfect based on the result. It was perfect insofar that is how people get taught to lay tackles from junior footy onwards.
He could have done something differently, but probably not without improperly doing the job he's paid to do.
I think it can. If you choose to tackle in a certain way and you're able to use your momentum and strength to safely bring the player to ground then your tackle is fine. If you lay an identical tackle but you've incorrectly judged the situation and you are unable to control their fall, then your tackle is imperfect. We judge something based on how serious the outcome is all the time and the AFL have been clear about how seriously they take it. If you can't safely make the tackle then don't make it. If you think you can, go ahead, but if you're wrong you can't hide behind your intent and actions not being malicious or inappropriate. Players are being put at risk of awful long term consequences, suspensions to prevent accidents seem completely appropriate.
I also don't think the rules need significant adjusting at all - they're exceptionally clear insomuch as the AFL wishes to protect the head and if your tackling motion places the head in a vulnerable position you're walking an incredibly fine line. This is reminiscent of when the rules were changed to prevent front-on contact when a player gathers the ball.