When you create a low res texture that's a decision, not an accident. Clipping is not intentional. It's when two or more elements not designed to work together end up trying to occupy the same space instead of having collision. As to which is more irritating depends on the situation and the person. It appears that SE are far less fond of clipping than low res textures.
Low res textures aren't nice but they're generally only noticeable from up close whereas clipping can often be easily noticed even from far away. From this my guess is that SE feel the potential horrific clipping from viera ears would damage the image of the game so they have opted to not permit most hats to be shown until, hopefully, a later date.
Low res textures are easier to handle from a design point of view because you can be strategic with where you place them. Clipping in the case of player characters is very dependent on the players' choices in how they choose to look which isn't easy to control without placing restrictions on what they can do such as not permitting certain hat models to be shown on certain races.
I'm not saying I agree with SE's decision to make most hat models invisible on the ShB races, I'm just trying to look at it from a designer's point of view.
Yes all of this would have been avoided had the new races' head issues been completely sorted out before they were released, but it's clear it would have meant that we would have gotten those races much later than 5.0. SE made the choice to release mostly finished races earlier than finished races later. I suppose they made that choice hugely because of the story they wanted to tell in ShB. Now that we are very late in the expansion we know that many major characters and plot points use the existence of viera and hrogthar to tell those stories.
Buuuuuuuuuuuuuuut none of this justifies giving the pre-ShB races 10 hairstyles while viera and hrothgar got literally nothing. Not even racial hats. There's no reason why SE couldn't shave off a few of those hairstyles to give something to the new races. The blatant uneven distribution of attention given to in-game rewards for heads is very frustrating.