This assumption is often lacking in nuance, even for a progressive like myself. Excessive inequality is undoubtedly bad. Debating quality vs quantity is a very different beast indeed.
To be fair, people might mean "excessive income inequality" and just shorten it to "income inequality", but I've found this to be less and less true in recent years.
Only to the extent that its the product of effort rather than innate factors.
Wouldn't this lead to people trying to take longer in completing tasks and making things seem "harder" than they are?
Abolish nature: then life will be fair.
We all, presumably, enjoy being human, and not animal. Man would not have come into existence if intelligence was not incentivized. The unusually smart and apt engineer, receiving a higher salary than the average or below average person, is less disincentivized to reproduce. If we were to equalize incentive for all the groups, smart and dumb, patient or impatient, we'd be equalizing their rate of reproduction, and forcing more incapable, experientially limited people into existence.
Wolves had no choice between being born carnivorous or herbivorous. When they attack our sheep, we kill them regardless.
The fairness you suggest is madness.
If we actually care about fairness, we should focus on social mobility and doing our best to create equality of opportunity. A lot of this begins with fixing public schools (in the US at least).
Whence come this desire to destructively level everyone?
Otherwise the engineer could spend his brain power on his own hobby projects while mowing grass for income.