The J&J vaccine having lower effectiveness makes sense. Unlike the mRNA vaccines which use lipid nanoparticles as their delivery mechanism, the J&J vaccine uses

The J&J vaccine having lower effectiveness makes sense. Unlike the mRNA vaccines which use lipid nanoparticles as their delivery mechanism, the J&J vaccine uses an adenovirus. Some fraction of the population has immunity to this adenovirus due previous exposure to similar viruses. That means the delivery mechanism won't be nearly as effective for those people. It also means that booster shots won't be nearly as effective since everyone who gets the J&J vaccine will be immune to the adenovirus. For higher booster effectiveness, they'll probably have to choose a different adenovirus. Obviously if you can get any vaccine, do so! But to claim that we can't possibly compare vaccines is silly. Yes the trials have differences, but they're not so different as to make us totally ignorant. We can use the trial data plus knowledge of the mechanism of action to make solid bets on relative effectiveness.