Theoretically, elixirs should be better. A mate has some reliable-so-far, properly working elixir cr’s and they stop better than the wilson family oro’s (2 sets in the go plus a third we since sold on), even if they are a bit more on/off. Neither oros nor elixirs have the best reputation for reliabilty of you believe everything you read on here, but both are rebuildable and pretty ok to get spares for especially since silverfish have taken on the distribution of formula. Anecditally it is easier to get the bleed ‘just right’ on oros too and the avid bleed kit you presumably have access too works on formula too.
If your k18’s work well and your elixirs don’t, I would either get your elixirs done under warranty (if you know how to bleed them properly and they deteriorate gradually over a few rides, it’s likely something wrong with the insides) or just ebay the elixirs as ‘unreliable’ and fit the brakes that work!