Recently I've learned from reading 1492 by Charles C Mann that's Europeans actually didnt have a technological advantage over American Civilizations, their armor was better than steel(All conquistadors switched to Incan textile armour over steel), Horses were not effective and natives adapted rapidly(Killing them in gorges, and in Meso America horses became useless as the men developed pikes and formations to trap them, after the first battle horses shock factor was gone and could no longer route Indians), and guns were less effective than bows / slings which could shoot over 100mph in the Andes. In most ways the Americas seem to be more advanced than the old world.
Was it really just Germs and Luck that lead to the overwhelming victories Spain had in the New World?
Not only to be sure. First, while the Spanish did indeed conquer large states they did this usually with the help of large numbers of native allies. Current research highlights that there was a complex interplay between having native allies due to internal divisions; epidemics; and some technological advantages among other factors. The impact of diseases would also be amplified through warfare, forced labor etc. over time. Second, large parts of Spanish America were not actually under Spanish control during the colonial period. So lastly, that "luck" is completely dependant on your own position and so a bit tricky in this context - ie luck for whom.
If you want to dig deeper our FAQ has a whole section on diseases in the Americas with this part especially relevant for your question:
Hope this helps!