I find that it is often difficult/immpossible to get a sense of scale.

The width and detail of streets is adjusted such that it is not obvious if I'm looking at things a few hundred metres apart, or a few kilometers! And there is no scale indication on the screen! I guess they want a "clean" look but it's not so helpful.

Take a look at Garmin aviation maps. You're offered only a specific set of scales (not an infinitely adjustable range), there is always an indication of scale, and the detail appropriately hints at the scale.