They aren't the same argument.

You're allowed to be offended if people from other cultures wear suits, because you're a person and people are allowed to feel how they feel. And an individual North American Aboriginal would be allowed to be offended because people from other cultures wear moccasins, because they're a person and people are allowed to feel how they feel.

But that offence, while legitimate, doesn't mean that the people who wear suits or moccasins are being culturally insensitive. British Cultural and Spiritual authorities don't explain to authorities of other cultures that they take offence to casual or commercial uses for these items. If your taking of offence is sincere (and I suspect that it isn't, but that you're trying to make a point), then you're more than welcome to explain to your non-British friends that you find them wearing a suit offensive. You're even allowed to choose to not be friends with non-British people if they choose ignore your offence, should you believe that the offence is so grievous as to escalate to that. And your offence, if sincere, would be legitimate. Similarly, if you befriend a Cree person gifts you moccasins and explains that they're prefer that you only wear them inside or one Saturdays or something, it doesn't make you culturally insensitive to wear them outside or on Mondays, although it might make your friend angry to hear that you disrespected their personal wishes.

However, if there were, say, a black immigrant to Wales who began to 'appropriate' the title "Sir" for himself without having been knighted, that would be culturally insensitive. British authorities have indicated that title has cultural significance, and should be held apart in a way that a suit needn't be. You're allowed to not take offence to this use, but it would still be an undue and insensitive cultural appropriation, on account of this.

Essentially, chances are good that you don't, personally, have the power, influence, or support that your personal convictions require the recognition of people beyond your loved ones. However, you're fortunate enough to live in a democracy! And as a result you get a vote for - and, should you so choose, the chance to run to be - an official to represent you in the cultural sphere, to determine and protect those British things which you think ought to be set apart. It would probably be too late to convince the world that wearing suits is culturally insensitive - Britain has had many years to make a claim and has, to the best of my knowledge, never officially done so. First Nations groups have indicated their official reproach to the misuse of headdresses since the practice was begun. Their cultural offence has the legitimacy of time, yours doesn't.

But, at the end of the day, it comes down to the fact that White Canadian leaders recognise and understand the reasons that Aboriginal Canadian leaders claim offence at the misuse of the headress, and they implore White Canadians to not misuse it. And we should listen. Because why would we want to offend someone just for the sake of offending them? It's not cultural disobedience to wear a headdress in contravention. You wouldn't be proving a point. You'd just be an immature, insensitive dick, demonstrating why our leaders are so tempted to crush us with unnecessary rules. We don't have crazy, overbearing rules like this because of the politically correct people. We have rules like this because of the asshats who don't understand the difference between wearing a suit and wearing a headdress.