Not necessarily. 50s / 60s US income tax is much, much higher than current rate. I just think the cycle of going up and down is extremely long.
https://commons.m.wikimedia.org/wiki/File:Historical_Margina...
https://commons.m.wikimedia.org/wiki/File:Historical_Margina...
These days people are paying more in real terms in aggregate.
Or was I unaware the widespread loophole back in the old days?
I think it's naive to assume that rich Americans back then weren't working the system. If it was so great, why do we tax different kinds of income differently now?
Lately though it seems like tax filing companies have been the ones primarily responsible for sustaining the complexity of the tax code - though whenever someone's particular benefit comes up that group tends to get pretty vocal (i.e. exemptions for SALT taxes and home owner/child credits)