The discussion section in the paper in your first link makes the case for the booster programs:
A booster dose significantly improves the quality and the level of the humoral immune response and is associated with a strong protection against severe forms of disease. An accelerated deployment of vaccines and boosters throughout the world is necessary to counteract viral spread.
This was consistent with the reduced neutralization levels they saw of the booster vs Omicron compared with booster vs Delta, and they cited an Israeli study Barda et al to support that this does indeed translate into clinical outcomes.
Could you please clarify this: "Altogether, these results indicate that Omicron is poorly or not neutralized by vaccinees’ sera sampled 5 months after vaccination. The booster dose triggered a detectable cross-neutralization activity against Omicron. However, even after the booster dose the variant displayed a reduction of ED50 of 18 and 6 fold, when compared to D614G and Delta, respectively."
Pretty much what it says - at ~5 months after the previous vaccination the performance against Omicron was poor, it was already reduced vs Delta at that interval as well, and since the vaccination isn't quite as effective against the Omicron variant as it is against Delta the end result was that at that point in the cycle it was barely doing anything against Omicron.
When you add the booster dose in it's more effective against Omicron (albeit still not as effective as it is against Delta),
At two doses + 5 months less than 12% of individuals were producing neutralizing antibodies sufficient for an effect against Omicron but at three doses 100% of the individuals they tested contained neutralizing antibodies:
Yes the antigenic differences between Delta and Omicron means the levels of these antibodies capable of neutralizing it is lower vs Omicron than the other variants but it's still sufficient to have a significant benefit in reducing the severity of the disease in those that get it, i.e. fewer people in hospital, fewer "severe" cases, and of course fewer deaths:
It might sound callous but frankly those who aren't sick enough to need hospital treatment aren't in much danger, and the "treatment" for them is to stay at home for 7-10 days and try not to cough on too many people in the meantime.
The paper on the use of therapeutic mAbs that a better "targeted" to Omicron than those produced by the immune response of vaccinated/convalescent individuals looks interesting, although as seen in the Schwartz article the performance against Omicron varies considerably among the different mAbs, arguably falling victim to the same differences in the new variant that have affected the vaccine performance. I'm not saying it's not worth pursuing - and certainly in the UK the NHS is using sotrovimab treatments (which seems to work against Omicron) for those in certain high-risk categories who have tested positive.
But there's some scaling issues to consider - sotrovimab is given on an IV over a 30 minute period plus a 30 minute monitoring period. So that's an hour per patient, plus any booking in and admin overhead, at a time when clinical resources are already at premium. A vaccine booster takes seconds to administer (certainly my whole appointment from walking in the door of the building to back out was less than 5 minutes including all the admin!), and can be administered by staff with a comparatively low level of clinical training and also be done pretty much anywhere (pharmacy, shopping center, gazebo in a carpark etc).
So the vaccines are already here, already tested, already mass-produced and already have a logistical infrastructure in place to give them to people on a massive scale. So, with the waning immunity offered by the previous two doses in the populations of places like Great Britain and France coupled with the highly infectious nature of Omicron a quickly spun-up booster program that provides not perfect but still pretty good protection to the general population seems to be a rather sensible route to take.