Your concerns just don't play out.
The problem with IRV is demonstrated in more detail here: https://www.youtube.com/watch?v=7Q7rzqJ0YS8
I think it's still better than FPTP, and it does let third parties at least get some attention. But there are other, better, systems. IRV has been adopted in a few places in the US, and then abandoned shortly after. I think systems like approval voting have a better chance of catching on.
But you can get more third party candidates winning (in single winner districts), leading to coalitions within parliament, which is probably what the parent means.