TLDR: if you need absolute accuracy, then yes RTK is absolutely worth the price tag.
I don't have anything to add to @Aruna 's response, but I can report I have been seeing similar results. If you need absolute accuracy and repeatability, RTK is pretty much your only option.
RTK will provide you with a significant increase in altitude tracking performance and remove the drift-y behavior observed when only using the barometers for absolute altitude tracking. I'd say that I've effectively observed the absolute altitude estimation within +- 20 cm. You just need to make sure your parameters are tuned appropriately (found here).