Modern day Physio's are hugely different to those of even 5 or 6 years ago, never mind 10 years ago. I would expect any professional physio to be able to give a reasonable prognosis, but following that, and taking into consideration that they are dealing with professional sportsmen, I would expect that the club would follow this up with expert opinion, to enable the physio, in conjunction with doctors/medical team to diagnose a course of remedial therapy and or recovery.
The physio's job is not one of just diagnosis, it is also to manage the injury and to ensure that the player gets the best and most appropriate treatment and that said player maintains this throughout the recupperation period. I think it harsh to wholly blame the physio for an incorrect prognosis, although if having identified the injury, the physio prescribes the wrong treatment then there is a case to answer.
Another consideration is that if the physio prescribes a course of treatment and the player/injury doesn't respond, then who is to blame, afterall we hear frequently of players not looking after themselves i.e. M O'M, JE, etc. You can lead a horse to water, but you can't make it drink and its always easier to blame a third party for your own failings, which I know some of our more UTOA's players are prone to do. Professional sportsmen and women, including our own players, have a duty to look after their own health, if for what ever reason they are reluctant to do so, then the physio, who is some way down in the management system, can hardly be blamed.