When renting a 1br costs as much as my mortgage on a 3br, I don't think that really tracks.

Depends where you live though. In the SF Bay Area, buying requires a monthly payment several times larger than the rent for an equivalent place.

Sure, but this is not universal.

I could have bought 15 years before I did. But because rent was less than half a mortgage (not even including maintenance), I was able to put that extra money into the market and save enough for more than a down payment on a forever home vs starter home when I was ready.

It’s certainly not like for like, but it would have been a poor financial decision to buy vs rent.

Where I live now this math is more or less inverted. Makes more sense to buy vs rent.

In the end your primary residence is a lifestyle decision, not a financial one. It’s not an investment in the traditional sense. It’s speculation at best.

"If I set up a scenario largely in favour of buying, then buying makes more sense"

I have never seen a 1br costing anywhere near as much to rent as a 3br costs to buy. In what markets is this even remotely close to accurate? Or are you just ignoring the cost of ownership entirely?

But a mortage isn't the only cost of owning. Property taxes, maintenance, possibly utilities.