So much back and forth on this debate and so much right on both sides.
As a pilot that's done both... I'll err on the side of saying the RFDS job is slightly less technically demanding.
(Perhaps just because you're left to do things your own way within the realm of SOPs)
The skills required, whilst very specialised, aren't beyond most pilots. Its just about exposure.
Conversely, airline ops aren't beyond most RFDS pilots or those of other backgrounds.
You don't go into the RFDS as an expert in the field. You learn as you go, just like anywhere else.
Retention though. This is key.
They need to pay somewhere between airline FO and airline Captain, which currently doesn't seem to be the case.
I find airline duties more demanding, the flying more demanding, etc., but we get a lot more days off and better pay to compensate.
The RFDS was more emotionally demanding, without a doubt. But also very, very rewarding.
But, the level of responsibility.
Id go back to the RFDS any day, but the pay cut is unswallowable, even as an airline FO.