Can mostly say the same for cheap anything, though. Depends what your use is.
Sierra is fine if you're going to mix it with grenadine and orange juice for a Sunrise as the tequila is a background player. But an El Diablo is very tequila forward (if made fairly short with limited ginger ale) and benefits from a good quality tequila.
And for a slammer I definitely want a good tequila as that's what I'm mainly going to be tasting. In fact, we finished off our Xmas bottle of patron gold as slammers last week.
I don't drink many straight spirits, most of them really don't taste good like that to me. There are some whiskies and bourbons I enjoy straight, and occasionally a dark and/or spiced rum, but mostly my spirits go into cocktails. Going to experiment with some sours recipes using the Jack, might tame the sweetness a bit.
I've sampled a few single malts and found them generally pleasant but unmemorable. I think I prefer blended, but maybe I'm just a cheap drunk. My fave going on for a few years now is Islay Mist, allegedly 8-yo and blended with Laphroig.