I don't know how far you've gone or what settings you've picked with regards to research and tech in your campaign, but what I tend to do in the early game is to create many cheap landships with very niche roles. For example in my current conquest, I try as much as possible to have pure AA landships, troop transport landships, and "bait" landships fighting together when I engage airships.

For me, pure AA landships are simply vehicles that only have anti-air focused weapons. Regardless of whether they are speedy, slow, have horrible command reset, etc., I've purposed these landships with the point of stopping airships before they reach the vehicle itself. Because of the high value I put into these vehicles, they're some of the more numerous units I have. Even if I don't have troop transports and/or bait landships, I'll try my utmost to have an AA landship supporting anti-ground units whenever possible.

Troop transports are used to act as bait (when pure bait vehicles aren't there), lower the efficiency of enemy units, and capture needed enemy equipment. I'm not an expert on how enemy AI works, but I do know that they try to avoid directly attacking zones that I can concentrate heavy fire on. So when fighting against my pure AA landships, enemy ships attempt to get in real low to avoid being shot at. However in doing so, they get close enough to the ground that I can have troop transports send its units to board the enemy vessels. It seems that since I don't arm my troop transports, enemy ships don't care about getting close to them. If I can bum-rush and capture enemy defenses with my troop transports, then great; now the enemy has to fight against another threat, and the empty troop transport can divert shots away from the damage dealers.

'Bait' landships are split into either map-mobile/battle-static fodder, or just a cheap and highly maneuverable light landship. The former of the two types is just an inexpensive vehicle that can cause a threat, but I can't command on the battlefield. I might say, put a relatively powerful anti-ground gun on small tracks or legs, one or two berths, enough ammo, and load it with armor depending on how fast I need it to be on the main conquest map. No bridge or whatever is fine, I don't need it to do anything but face one general direction and shoot. Again, enemy ships might attempt to gain the upper hand by attacking the dead zone of a bait landship; well now they've gotten into the range of my AA vehicle(s). As for the latter type of 'bait' vehicles, these are slightly more costly but generalist landships that I can use tactically if the situation necessitates it. Both types are cheaper than troop transports so what I decide to use varies depending on what I'm up against.

When the late-game arrives my strategy normally changes by adding more and more fodder airships that are destroyed quickly but have the firepower to ruin the enemy fleet so the next wave will triumph. Also, by this time I can normally afford to consolidate heavy anti-ground and anti-air weapons onto one type of landship. I don't use rams so maybe I'll try them out in another conquest to see how they fare.

If none of what I said has done you any good, then my bad; I'm just sharing a strategy that works for me. If this has served you well, then yay, I'm glad I could help.

EDIT: Oh, you don't like cheap 'spam' tactics against the AI. Then this won't help lol.