For me, the less between my eyes and the card, the better. Toploaders accrue scratches and fogging easily, and that, compounded by the weight and cumbersomeness of that style of binder wouldn’t jive. It’s just excessive to me.
But to answer your question, the only way cards get dented is from the pressure of the pages in a circular ring binder being pressed under/against the ring. When a card is dented on the bottom, it’s because it was sitting over the top half of the ring curve, and usually pressured by the weight of the binder cover. When dented on the top, it is because in the same fashion it is tucked under the bottom curve of the ring and the other pages providing that pressure. As kids we saw this with overstuffed binders. This is primarily the issue with circular ring binders and overstuffing them / not storing correctly. Even if circle rings aren’t over-capacity, the pages can still get tucked in a sideways U fashion, just from th way it can be closed, and get pressured and dented. It’s just the way those binders work. Not meant to store cards.
Example of how cards get dented, don't be like this guy
Top pages will get cards bottom dented, bottom pages as you can see will be top dented from being under the ring curve and weighted by other pages etc.
This is why the only way to seriously consider storing valuable cards with a ring binder is a D ring binder. Stored flat, not like a book on a shelf. With a D ring, the pages, as long as they are not over capacity in relation to the binder size, will always be aligned flush with the straight line on the ring, and not ever get over or under the curve of a circle ring. The pages will be stacked perfectly, more or less, as if one were to stack those pages on a desk without any binder. And yes, when I flip through them, for good measure, I do not carelessly drag them over the ring. I turn the page with care so that it goes up and over all the way. This method cannot dent cards. And it allows you to have transparent pages, seeing the backs of your cards, and maintaining that nice aesthetic.
Quality, sturdy D ring binder and nice 9 pocket pages (for me nothing is better than black duck brand pages, crystal clear, nice glossy feel to them) will run you a mere $10-15. When I’m not using the standard zipper binders that have black pages, I use my D ring binders, particularly when I like seeing the backs of cards (like is with the case of old back).