re: Imagine the US government’s only source of revenue being tariffs.

Many professional economists blame high tariffs on the Great Depression. I have found none of the mainstream economists that tout conventional wisdom on the reasons for the Great Depression mention income taxes.

As income taxes came on line tariffs did decrease. Before the Depression tariffs made up approximately 15% of federal tax revenue and the remaining revenue was made up by income taxes and other sources but mostly by income taxes. Prior to the 16th amendment and income taxes, tariffs made up most of the federal tax revenue. After the Depression and into 40's tariffs made up and continue to make up 1 to 2 percent of federal tax revenue.

Leading into the Depression it wasn't just tariffs that caused the Great Depression. It was the total impact of high income taxes combined with high tariffs.

Total taxes are the overarching issue.
The secondary issue is the type of tax and those fall into two broad categories, regressive taxes and progressive taxes.

I personally favor regressive taxes like the Fair Tax, sales taxes, VAT taxes and tariffs over progressive taxes like the income tax.

Regressive taxes tax consumers. Progressive taxes tax producers.