I can’t speak to the RDS80 as I’ve never used that model. But I own the icon nano at home, and have used JBC (T245) and Ersa icon 1 and 2 extensively at workplaces, and have also used various Weller, as well as older Pace cartridge systems (TD100). At my current job, when I was allowed to purchase a new soldering station of my choosing, I selected an Ersa icon 2V Mk II, which I have now been using for a good year and a half.
It sounds to me like you’re not getting good heat flow between tip and joint. Are you comparing the stations with the same style and size of tip? A common problem is people using too small a tip.
The icon series tips certainly don’t have a “massive” air gap between heater and tip. The whole reason Ersa has been able to avoid (or delay?) switching to cartridge heater tips is by having close tolerances between heater and tip. It’s not
quite as good, but in practice of everyday soldering (of anything that crosses my bench, from tiny SMD to very large connectors and multilayer PCBs), you don’t notice it. What matters is proper tip selection, tip care, and technique.
To be sure, on really heavy joints, there is a difference between the icon nano/pico and the “big” icon stations. But even so, I’d say that proper tip selection makes a much, much larger difference.
430C is an insanely high temperature. I bet you’re using too small tips, then cranking up the temp to compensate, which then causes tip oxidation, which reduces thermal conductivity! (For reference, on Ersa, JBC, and Pace, I usually use around 320-335 for leaded, 330-345 for lead-free. The only exception is when using the extremely fine 0.4 and 0.6mm tips, because thermal conductivity to the working end of such fine tips is terrible, so the working end is always many degrees cooler than the set point. Larger tips don’t have that issue.)
Just yesterday, someone posted the following white paper in another thread. I highly suggest you read it, because you may identify some ways you may have unwittingly sabotaged your soldering performance.
https://www.newark.com/pdfs/techarticles/oki-metcal/extendingTipLife.pdf