You're mistaken. Please get the booster.
The Omicron variant largely evades immunity from past infection or two vaccine doses according to the latest Imperial modelling.
www.imperial.ac.uk
Well they are and aren't.
Omicron evades them yes, but the likelihood you'd actually get anything worse than a cold from Omicron if you've had natural infection and two vaccine doses is extremely, extremely low. Which I believe is what the poster you have quoted is saying. The T-cells and antibody response will still be there and work just fine.
I'll still be getting my booster in a few weeks, when it's been a month since infection, but frankly I'm only doing it for ease in case they bring in more rules. Having had COVID twice, one of those times being Omicron, and being double jabbed, I don't see how having a booster is going to significantly help me. I'll probably be infected again in 6 months at this rate.
Obviously I agree with you that it's just safer to get the booster