Yeah I see what your saying and agree with it. There is utility in the rule under the proper circumstances and when it is used in good faith, but it is a slippery slope to frustration. Particularly for other fans (and players) that feel their teams become a victim of it. Like you mention, Kucherov practicing 6 weeks full contact and then stepping in the first playoff game and playing to the level he has been from then on is suspect, or at least I think it is. That said, I am not a doctor, trainer, or a person has had to go through that kind of surgery.
The answer is probably not in changing the rule, but ensuring the proper checks and balances are in place to ensure the integrity of the rule. I know I have seen people say that the NHL could have investigated it if they felt it was cap circumvention. However, does the NHL really have the authority to force a player to submit to an independent medical examination in those circumstances? I really don't know the answer and would be interested in what it is but I would be surprised if the NHLPA didn't have something to say about it. Further, any opinion the NHL does obtain from a doctor would without a doubt be countered by team doctor opinions and independent specialists the team chooses to retain. I guess the NHL may have the power to deem them ineligible for the LTIR if they could get the evidence, but I think getting conclusive evidence would be the hard, if not impossible part.
Anyway, I agree the rule is useful when used properly, but I think the enforcement or checks and balances surrounding it may be lacking. Then again I guess we don't know what happens behind the scenes and for all we know the NHL did investigate.