What you call "conclusion" is probably a forecast, since we're talking about the future, right?

In some cases, yes, in other cases, it's already observable as an ongoing process (I brought up reef ecosystems before because they're a particularly visible example of this.)

Recent ice ages have advanced and retreated very quickly on the evolutionary time scale. Earth's various ecologies survived, for example, the last ice age just fine and the glaciation looks to me to have been MUCH more disruptive for temperate zones than a couple of degrees of warming are likely to be.

The original onset of the first ice ages was indeed quite ecologically destructive and qualified as a substantial mass extinction event (although it was still much slower than anthropogenic climate change.) But virtually all species alive today are ones that have persisted through multiple glaciation periods. The flora and fauna of today's world are denizens of the ice ages.

I should note that all of the points that you're raising have plenty of representation in the existing literature on climate change. It's definitely not the case that scientists don't think of these things. But these points are followed up with more research to determine what kind of expectations are warranted, and in some cases they're ones that merit concern.