Hmm, not sure having civics do similar things to each other is good - i.e. alternative caste system as you're saying.
In any case slavery is a well-designed civic in many ways. The idea of converting food into hammers (or something) is required, especially early on when the standard map types tend to leave us with too much food which we can't use because of the happy cap. Also as a concept working citizens to the death makes sense (at least for construction work anyway, not so much for training soldiers
) And letting you sacrifice virtually your entire empire population for a concerted war effort later on is a good option too and gives you a bit of a chance against crazy high-level AI bonuses.
My problem is the micro. Some simple changes would really sort that out though:
(1) Remove the penalty for whipping a build with zero hammers invested. This would mean you could go into a city, do a load of whipping in one go, no need for a spreadsheet and calculator, then get back out to the map and grand strategy and let the city regrow on its own.
(2) Allow partial-build whips, not just to complete a build. So then none of the hokey overflow shenanigans we have to get involved in to try and get round the system. 1 citizen
death equals N hammers into the current build, simple
(3) Too powerful? Yes definitely, so balance by reducing the hammers per whipped citizen. 30 is too strong in any case already. Try 20. Playtest. Adjust. Repeat. End result: perfectly balanced, simple-to-understand, minimum-micro slavery civic, and not to drastic a change from the current situation.
But anyway there are tons of "fix slavery" threads and other ideas - some people even want more micro
so you can't please everyone! Also "fix serfdom" which is the other big balance disaster in that column ... (another purely numerical factor which they might have playtested and fine-adjusted a bit better).