If you want to just discount the price of CAs and BBs and leave everything else the same, go ahead! I still won’t buy any CAs, and I’ll still rarely buy BBs, but I don’t think your changes will hurt anything.
The point of giving transports a defense of 1 is to eliminate the concept of the “defenseless” unit, because that adds more rules to the game for insufficient benefit in fun and strategy, and to make it easier for players to build very small navies (potentially just a single transport and nothing more) in minor theaters. I think the cost structure I’m suggesting works without it, though – if you like defenseless units, just drop transports back to D0.
The reason for repricing everything is to try to set up a more interesting thematic difference between SSs, DDs, CAs, and BBs. SSs are small and cheap and good at offense. DDs are small and cheap and good at defense. CAs are medium-sized ships that add good punch to a fleet but are over-priced to use on their own. BBs are big, expensive ships with a much higher offensive value than other ships, but are likewise over-priced unless you can support them with lots of escorts.
As SS Gen so kindly and gently points out, though, we’re all wasting our time – nobody is going to playtest this stuff.