In Canada we have a tax free savings account that lets you invest about 6-10k a year entirely tax free (it varies from year to year). The issue is that it does not allow you to leverage your investment or use margin. So to get around that every year I dump my entire 7k into TQQQ and UPRO 50/50 and have done so since 2013.

I don't see why this would be a bad idea and this article seems to be fairly poorly written. In general there is nothing wrong with putting some of your capital in a tax advantaged account into a leveraged ETF. No one is suggesting to dump all your savings into it, but putting some ratio of your earnings into a leveraged ETF allows you to indirectly maximize your contributions.

I'd definitely prefer to use margin directly through my broker, it would be cheaper and less risky than an ETF, but the law is not setup to allow me to do so in the various retirement or tax advantaged accounts, so instead I use this as an alternative.

For ordinary investment I think using some leverage is smart, especially if you're younger. Take something along the lines of 2-2.5x leverage until you're in your 40s, then start scaling it back as you get closer to retirement age.