Both articles run 100% in opposite directions, each based off of a single person speculating.
Here's the good news. The one that thinks Omnicron will "Overwhelm" the world is basically saying it will do so much in the same way Delta did and he thinks vaccines will hold up at a pretty good level. This means even he thinks that people that have been fully vaccinated or have antibodies from previous infections will generally do well.
It's also worth noting that he is comparing the timeline of Delta in March to Omicron right now. In March Delta was already well established globally with about 10% of infections. Omicron is less than 1%. So the 6 month timeframe is the much more likely scenario in that 3-6 month guess.
The one point that is probably the most accurate is the undeveloped world is in trouble.