"There is a lot of research that suggests late weaning can increase allergies, so it would be surprising that early introduction of 'non breast milk' would cause the same problems."
No, this is not accurate, or at least it is misleading. There is some contention around whether babies who are at a higher risk of coeliac disease should be offered wheat earlier or later, and there is evidence either way with research ongoing. But this is a specific issue and not "a lot of research that suggests late weaning can increase allergies". Actually for MOST babies later weaning is considered safer if the baby is exclusively BF and for A VERY FEW babies there is some discussion of ways that food should be introduced.
OP, you are right, the evidence on the introduction of formula in this way shows that it can trigger problems and this is why it is important WHERE POSSIBLE to avoid any formula, especially after a CS because the baby isn't populated with the mother's bacteria as during a vaginal birth. However. or rather, HOWEVER. No matter what we do we balance risks. As has been pointed out, if there was a low glucose problem then this did need to be treated and therefore formula was given as a medicine. Like all medicines there are the potential for side effects, but the risks of the side effects are generally considered lower than the risks of not treating and in this case it's very likely that the medicine (formula) meant that more serious problems were avoided.
The general understanding is that it takes about 2 weeks to repopulate after one feed of formula (or other non-BM foods) but yes, it's more likely to be a problem in the early days and I'm not going to back away from that. But, what you have done is taken a difficult start and done the only thing realistically possible (treated the low blood sugar with the only treatment you had) which can cause very serious problems if left untreated, then moved on from that and done one of the single most important things that you can do for the life-long health of you and your baby. The risk from the formula given is, honestly, tiny. Really small. The risk of not treating the low glucose, if a genuine low glucose problem, was high.
The paed should have suggested donor milk and hopefully people reading this will learn that this is an option (www.ukamb.org if they are in this position. Informal donation from a friend or relative is also possible (your baby, your choice). This would have resolved the risk of the introduction of cow's milk protein. But the effect of cow's milk protein can be cumulative, meaning the more that's given, the worse the risk so the risk here is TEEEEEENY.
I think you should continue to proudly announce what you have done. :) :)