Have you ever compared with actual printed paper?

Depends what your reference is. E-ink displays without a lot of layers (especially Carta 1250) have pretty good contrast, on par with matte paper. Some devices with a thick frontlight layer and a Wacom layer and a touch layer are less impressive.

My Onyx BOOX has at best a background comparable to very dirty newsprint.

I find myself reading with the frontlight on under most indoors circumstances, unless I'm in direct sunlight. With the frontlight, it's fine. Text may be somewhat more washed out, but that bothers me less than a darkish background.

Under sunlight the contrast is actually about perfect, as white paper tends to be too blindingly bright.

My tablet has several layers: capacitive touch, Wacom, and frontlight, all of which probably contribute to the lower contrast.

Mind: I'm addressing your "bad contrast" question. I find the trade-offs reasonable, and for reading ebooks (as opposed to Web browsing or other app use), the frontlight battery consumption is quite reasonable.

If I'm just using the device casually (e.g., listening to podcasts or checking something quickly) it's fine to use w/o the frontlight, but for immersive reading I'll either have a strong reading light, frontlight, or head for a convenient sunbeam.