On an (aternos) Minecraft server i had used a command to avoid pigmen because the pigmen were always aggravated if you used a weapon (servers fault, not game) and a huge amount of ghasts were spawning, about 3 or 4 times more than usual. I used the command /tp @e[type=minecraft:zombie_pigman] ~ -255 ~ in a repeating command block to deal with the pigmen.
MC-154167
Ghasts spawn excessively without pigmen
Resolved
Invalid
0
As far as I know, ghasts share the mob cap with pigmen, and hence every time there are still mobs free to be spawned (aka, the mob cap is not filled), it will try to spawn new ghasts and new pigmen.