It's a trope among liberals in the US that taxes are too low, just look at the marginal rates, they used to be 90%! If they used to be 90%, then it's perfectly reasonable to raise them to 35%... I would guess you've heard this quite a few times (even if you don't agree with it, it's a very commonly presented argument), whether you realize it or not, and you are just repeating it. This is largely how political opinions are formed, people pay attention to the side they want to agree with and they internalize the one sided, often easily debunked arguments that side presents over and over and over. It's a form of voluntary brainwashing. As you said, it's not completely obvious what is true here, but if you ask around you'll find that people have very strong opinions about it and are often willing to argue at great length despite having literally zero information for or against.
The tribal point was that I got 2 responses saying 'technically we aren't at the absolute peak tax rate' based on the graph I posted. Instantly people wanted 'taxes aren't at an all time high' to win, and assume this is because their 'tribe' is the one that wants to raise taxes. If you look at the graph we are very nearly at the peak, and certainly from a historical perspective we are plateauing very near the peak. That's not arguing in good faith to chime in that OP was wrong because technically we are a smidgen below the all time high, and OP said 'all time high' rather than 'near the all time high', so they get an L and their side loses and we can just pretend there's no more detail than that.
Years ago a FB friend posted something along the lines "every country where the debt is 100% of GDP ended up with runaway inflation." (It's been a decade; I've forgotten the exact details.)
It was easy to point out that the US had >100% ratio in the 1940s, due to WWII, without the consequences he postulated.
I then found it was a "tribal point" going around, that he was repeating without investigating.
This claim that taxes now are the highest ever felt like the same sort of "tribal point."
How does one challenge an seemingly wrong assertion without also being labelled "tribal"? Especially in a field so contentious as this where there are position papers upon position papers for- and against- just about every point you can think of.
FWIW, I think the premise is flawed. Rich people put their assets in trusts and foundations, which are not subject to the same taxes, and yet controlled by the them and their family.
(For example, "Patagonia Billionaire Who Gave Up Company Skirts $700 Million Tax Hit; Founder Yvon Chouinard structured the transfer of his firm in a way that keeps control within the family and avoids taxes." - https://www.bloomberg.com/news/articles/2022-09-15/patagonia... )
Because those savings aren't paid taxes, they don't show up in charts which summarize only those taxes paid.
So when "liberals in the US [talk about how] taxes are too low", I believe it also refers to the legal techniques rich people use to avoid paying taxes, including through laws which were specifically created for this purpose.
I agree 100%, I would guess that he was probably repeating 'taxes are the highest ever' that he heard on a conservative talk show or FoxNews or something. I think the taxes as a % of GDP data is not perfect but it's at least a fairly reliable well studied ratio that avoids the problems with the details of tax rates as you point out, tax rates don't correlate well with taxes paid so looking at them is misleading at best.
The tribal point was that I got 2 responses saying 'technically we aren't at the absolute peak tax rate' based on the graph I posted. Instantly people wanted 'taxes aren't at an all time high' to win, and assume this is because their 'tribe' is the one that wants to raise taxes. If you look at the graph we are very nearly at the peak, and certainly from a historical perspective we are plateauing very near the peak. That's not arguing in good faith to chime in that OP was wrong because technically we are a smidgen below the all time high, and OP said 'all time high' rather than 'near the all time high', so they get an L and their side loses and we can just pretend there's no more detail than that.