In terms of IPCs, you will be buildling other units more than infantry as the naval nations. Usually as stuff like UK/Japan you’re busting out like 1 inf per 1 tank, and quite obviously the tank costs you more, so I would think that overall you’re spending more on tanks since you have to consider the IPC cost. Do you honestly load up transports with 2 x infantry? Thought not.
Take into the account the actual cost of the unit, not just the numbers you purchased. Battleships cost 8 infantry, so you can’t just say oh I’m buying 3 infantry compared to one battleship therefore infantry is better than battleship in value. You have to factor in IPC cost.
I’ve never disagreed with infantry as the most valuable buy for Germany/Russia, but I heavily disagree with the other 3 nations who pour much more IPCs into naval units and supplements to go into transports. You can’t just count the number of infantry, you have to count their cost. In numbers they aren’t built more than other units as the naval nations because you’re building 1:1 ratio with tanks. And if you look at the costs entailed, they’re skewed in favor of non-infantry units as naval nations.
Infantry are really great for advancing slowly since they’re able to hold the territories they captured with cheap cost, and really necessary for defense for Germany/Russia, but I simply observe that more IPCs go into noninfantry as the other three nations because of the transport limits and heavy naval buildup costs.