"It's not neat and tidy so it must be genocide" - not sure that's quite right.

In this case, it was genocide.

It definitely was. There were at least sometimes extenuating circumstances though.

My sense is that in the US and Canada settlers found a great deal of "apparently" uninhabited land, largely a result of the diseases that had swept through because of earlier contact, decimating the existing population.

My guess is that had disease not done its work, the European settlers would have found it much harder to displace the existing inhabitants.

I have yet to read 1491, but yes I imagine that it would have been much more challenging without that first strike. But the weapons capabilities of the europeans were also going to make it happen one way or another.

America is a big place, populated by a lot of different people. Some of those were in fact victims of a genocide by European colonists. Others were allied to the European colonists from day one, and were instrumental in defeating/exterminating their indigenous enemies (see e.g. Tlaxcallans). Most of the victims were decimated by Eurasian diseases well before seeing any European with their own eyes. So presenting colonization of America as a "genocide" is every bit as selective and simplistic as what you're old enough to remember being taught, just in the opposite direction. The history of Americas is much more interesting and complex than all that.