Extra conditions like this mean that the path we took would be rarer but doesn't necessarily make life any more rare. There could be plenty of other pathways to a stable carbon cycle. Or it might not even be a prerequisite, you could imagine a scenario where life gets a foothold then instigates the cycle itself.
We just won't know until we've found something. And for us talking now we probably just won't know.
Especially because they may all just be indicators of something else. I've heard magnetic fields, moons, and plate techtonics are all important, but that really could just be "the right kind of planetary collision not too long ago"
Sure, but then add the evolutionary path on top of that. We had hundreds of millions of years of dinosaurs and no evidence of intelligent life.
Then you've got to consider that Earth is basically approaching its twilight years. The planet is 4.5 billion years old, macroscopic multicellular life is 600 million to a billion years old. Humans have been around for 100,000 years. In 500 million to a billion years Earth will become uninhabitable again.
Oh and our sun is unusually stable.
Throw all of this together with an added "right type of huge planetary collision" and I feel like you're writing a lot more zeros into that probability.
Of course it's possible that life could take a different path, but there was a lot of opportunity on Earth and it took a long time to get there.
All that comes after the planet is suitable for emergence, which is the focus of the conversation. We can reinvent the drake equation all day if we want, but yeah, definitely, those are more factors to consider.
There are very few atoms that allow for the complex scaffolding for shapes. Many atoms are too large (and thus bond too weakly). Silicon is interesting, but it has some difficulties.
My organic chemistry professor always liked to point out that while CO2 is a gas that is easily dealt with following metabolism, SiO2 - silica/quartz - is most decidedly not a gas. Add that to the list of challenges for silicon-based lifeforms. Not to say that it isn't possible, but it does constrain the solution space somewhat.
We just won't know until we've found something. And for us talking now we probably just won't know.