Agree. The simple analogy is third-party liability insurance for your car: you have to buy it from a private company; the benefit applies mostly to other people (or society); you are required under the law to do it whether you want it or not; pricing is often not 'fair' from the perspective of people paying it (i.e. they think they're never going to get into an accident and most in fact do not); and it absolutely does not matter if you think driving is essential or not (as some people in rural communities complain, driving is more essential in some places than others), you still have to pay it. (Of course like any analogy it's imperfect but I think it's a useful analogy)It is the law; it's an order under the Quarantine Act. I'm not sure why you think it's any different.
Not everything that is perceived as unfair (or even is unfair) is a human rights violation. That's not how rights work (in Canada, anyway).
I think it would be great if they gave at least partial refunds for those that are allowed not to stay the full three days, and made some other changes - I don't think anyone is claiming that this policy is ideal or has been well planned or administered. Personally I think it was rolled out mostly due to political pressure - primarily the provinces blaming the feds for not being more strict - and without the detailed analysis to show it was fully necessary in the form it was implemented.
Anyway, complaints about aspects of it don't invalidate it legally, and it's far more likely it will be changed as the covid numbers change than due to to these (from what I can tell specious and doomed to fail) legal challenges.