I think your reaction to very dark foliage is natural. We will not all perceive attractiveness in plants the same way but I would bet that many would not be over the moon with anything darker than a copper beach. Personally I have always regarded very dark foliage a passing novelty.
As written here, that is only my view and I would not presume that it was shared by others.

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I use the dark foilage for drama. Like Black Magic EE next to white or silver foilage.

Same with bronze or gold put a blue hosta or blue flowers and the gold comes alive.

I dress my garden like I dress myself. Unless I am in mourning I never wear all dark clothing with out a scarf or shirt to give it a lift.

Purple and bronze foliage continue to be very popular foliage colors here in California, where the clear light year round really can show them off to perfection. Purple leaf Plums and Purple Smoke Bush will always be popular here, and deep purple red foliage of Phormium 'Guardsman' or Loropetalum chinense or Cercis 'Forest Pansy' will stand out in any garden if planted against a green backdrop, and the huge foliage of the banana, Ensete ventricosum 'Maurellii' is pretty hard to miss in any garden where this beauty is planted. I do agree that burgundy foliaged plants like some of the Heucheras can disappear if not accented or backdropped with lighter foliage or hardscape.

Not all dark foliage disappears. Perillia frutescens shines in any setting.

Dark foliage adds contrast, interest and enhances the impact of surrounding colors. Here it's Kale "Redbor" and "Crimson Pygmy" barberry helping out Bouvardia ternifolia.

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I couldn't say it better- dark plants are about contrasts and a lively palette of color offset with dark or quiet areas to bring attention to the lively color. It works in a painting and a garden. Look at the art in your home. See the shadows? They are not the focus. They serve the purpose of focusing you eyes on the focal point. To take away the dark is to take away highlighting of the bright.
I would agree with you about brown foliage. Unless is has purple overtones it is nasty and deadish.
Karen

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