Do you currently warmonger with Zulu Longswords? They feel plenty strong to me and they would just as strong as they are now.So are you going to build swordsmen and then have a mix of nonunique longswordsmen and Impi, or build only spearmen and hurt your warmongering ability early? Both situations feel bad.
I also can warmonger early on just fine without swordsmen. I think getting your powerspike a lot earlier is a huge advantage.