"How is the infantry going to get around without armour? In particular, how are they going to be protected during the advance?"
Over time (or rather history) the weapons mix changes. Invention of the machine gun led, eventually to the tank - but things never stay static. It may be, that in some areas, driving around in a very large, expensive tank is no longer a great idea (think Battleships post 1940). Dispersed infantry are a lot harder to hit with drones etc and the cost of using smart air launched missiles to attack small groups of infantry is prohibitive.
The pendulum will probably swing back once cheap anti-drone defences are available - I don't think tanks and armour will disappear at all - but I think they'll be less important for the next 20-30 years