We have never seen another living planet so we don't know what to expect from one. I touched on this originally but I'll be explicit now: the fact that we can't create a closed ecosystem even given a working example and diverse raw materials is a powerful indicator of our ignorance about the contours and possibilities of life.
I'm not saying it is impossible, but I'm saying any confident assertions about its possibility, much less how "easy" it is are fantasy if not pure hubris. It's quite possible that no level of advancement will allow for even merely interplanetary life.
This assumption is exactly what I am challenging: that there is such a thing as "general suitability" to life.
We should be open to the possibility that a living system is only compatible with the specific circumstances it emerges from. We've seen nothing to indicate either way, of course, not having seen any other life. But we should not so comfortably assume it's a transferrable process.