It’s always been known bees will, in the absence of flower pollen, collect all manner of powders including brick dust, rust spores etc. That doesn’t mean it does them any good. Similarly, patties of assorted mush may be put on and disappear over time but whether that is always beneficially consumed and becomes more healthier bees is often less proven.
Historically, in the UK the wide seasonal variety of naturally occurring trees and plants And crops I suspect made feeding supplements unnecessary. Whether that is still true today is a more moot point. As Donald Sims observed in “Sixty Years with Bees” areas such as Foxton where he lived (once known able to support a host of colonies) by the time he moved there were barely able to support even a few garden hives.
This replicates in miniature the situation I understand with some huge commercial operations such as in the US, where literallly thousands of colonies are kept alive and built up for mass pollination contracts on syrup and sub. for significant periods of the year. Interestingly Sims used sub patties. I suspect it is this sector that provides the bulk market for commercial sub products and pays for the advertising accordingly. Randy Oliver’s study was obviously interesting but as I remember it, it was deliberately carried out at a time of year and in a location where natural pollen was known to be either absent or inadequate. Despite applying many kg of patties, when natural pollen (from Alder) become available the upturn in colonies was universal.
As a hobbyist I agree with Nigel’s point that if your bees are located in an inadequate forage area - common sense says move them. In practice this may not mean miles away - anybody looking at pollen loads has probably noticed bees can be surprisingly local in their pollen foraging preferences. A few hundred metres may apparently help.
The only other big issue is weather. All the pollen in the world is no use if they can’t access it due to excessive cold, wet or wind. Hence I might be as concerned at the prospect of a wet summer to need to feed pollen, rather than just the syrup commonly suggested if stores are low. To date, this has only been in hindsight, so not much use to the bees.
We all have a commendable wish to ensure our hives flourish, but to date I have done okay with not using subs. However I do know I am very fortunate to have a good succession throughout the year of natural and cultivated pollen sources very locally. Not to say they might have done better if I had done differently, as with so much else!