I consider myself pretty allround, but the first time I visited a local crag I stood on a sling to get to the anchor of a bog-standard, middle-of-the grade 6c.
If you need to stand on a sling to get up it, it doesn't sound much like a bog-standard middle-of-the-grade 6c to me.
I've done it since, it's fine at 6c when you get used to the style
