For 1) and 2) you are completely right -- Telerik should not decide for a developer how a thing should look, if that developer has something else in mind. This is why we provide enough selectors for developers to change the look and feel of our controls.
For 3), having in mind that the current skins are done mostly with images (background images) and not using the CSS specs to it's maximum due to legacy browsers, inherited line height is not always a good thing, as it will either squish or stretch the looks of the panelbar.
I understand your request and the reasons behind it, however, this particular behaviour is is relied on by other developers and should we change this behaviour it will break in every such case.
We could perhaps consider an additional trigger, say UseDefaultLooks="true" or something like it to switch "on" or "off" the styles in question. But we need to consider this very carefully, as we do not want to break anyone's code / looks.
the Telerik team
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