Source? The first couple of graphs here: https://en.wikipedia.org/wiki/Income_tax_in_the_United_State..., suggest otherwise. We've rarely had income taxes as a higher percentage of GDP than we do now.

If you just look at federal income tax (not payroll tax which is stacked on top of it, and not state and local taxes on top of that), the long term trend is downward since the end of WWII.

It makes complete sense to not ignore them though.

State and local taxes have nothing to do with the federal deficit, so excluding them is obviously correct when talking about the federal deficit.

Social Security is the bulk of payroll taxes, and most of the increase in payroll taxes, and remains self-funded (though that would cease to be the case if the trust fund was to be exhausted and full benefits maintained.) So it makes sense to exclude that.

But payroll tax also includes Medicare taxes (the payroll tax portion, not the additional income tax portion on certain income not subject to payroll a tax imposed under the ACA) as amuch smaller component, and while Medicare Part A is self-funded, Parts B and D have significant general revenue contributions as well. But Medicare payroll tax hasn't changed significantly (and the share of GDP subject to it has dropped as returns move out of labor and into capital), so if you kept it in but split out Social Security for the reason above, it wouldn't change the declining trend shown by income taxes (except to enhance it).

So, again, the federal deficit is driven by declining federal income tax share.

To some extent. Military spending as a % of GDP isn't that high, ~4%...but may still be a bit higher than usual for relative peacetime.