I'd say there is a gradual progression whereby each bit of additional automation reduces pilot workload.
Nothing does as much as an autopilot. But even then it is a pilot workload issue. I would not depart of any significant flight if the AP was duff, but once got a failure on the way to Greece and had to fly by hand most of the way there and then all the way back. It was not an issue but one cannot easily take pictures, have a pee, mess around, etc. The flight is still safely possible, of course, but it isn't fun anymore. I was lucky on that one - had a passenger who could hold the wings level, etc.
And in difficult IFR conditions, a lack of an AP could push a less than current pilot outside what he can handle. Some PT ops require an AP for this reason - even those pilots are gold plated ATPLs with a medical every week
it is recognised they are not superhuman and the pilot workload reduction is a vital safety improver.
I think too many pilots do fly without a proper systems understanding, but this has always been the case. I recall talking to one pilot who thought a VP prop was driven through a variable-ratio gearbox
Now we have the same at a higher level - pilots who fly with a G1000 and don't know what most of the features do. This was just as possible with a GNS530 for example but there is a difference: the 530 was probably flown by the owner who probably did read the manual, whereas a G1000 could likely be in a DA40 flown by a renter.
I don't think an IFR GPS is extra work as such. One loads the route before the flight, but (especially if one has an AP) one can do this during the flight too. The level of pilot interaction with a GPS enroute is really minimal. The real problem would be if one didn't understand it and tried to work something out when airborne.