I don't think this is true, actually I think you are being dishonest here. I am pretty sure the primary resistance to greater use of the mRNA tech were problems with serious side effects and the thought of lower dose use in the vaccines had been pushed because it was lower dose.
Honestly I think you sound very naive and trusting of biotech. I am not saying Moderna or Pzifer are dishonest, but the technology is much more invasive, you could say, than conventional vaccines and while in theory it should work, there are in theory a lot of things that could go wrong, 3-4 months of phase III trials is not long enough to elucidate major long term issues of any kind and I really do not think there has been extensive enough work to verify much of anything to date. Feel free to provide evidence contrary, but I believe you are overstating your claims here. Any chance you have ties to Langer/Springer or BioNtech?
Overall I am hoping things work out, but the whole concept has for year wrung of classic and naive overzealousness on the capabilities of biotechnology while completely ignoring the complexity of the systems being targeted and the problems that could arise. To answer your question, yes, sometimes we should wait 40 years to be certain of things...such as trying to answer the question of whether or not we should experiment with new and highly complex technology (and it is, even if it seems simple) on our children. Go ahead with the old folks, as it seems safe enough in this scenario, but if they force this one on the kids there should be massive resistance. Again, I am hoping for the best, but in the end we are essentially conducting a massive experiment on the global population, which honestly could pose a much greater risk to humanity than the corona virus we are fighting.