Is there such thing as being 'too good-looking' for someone?

Yes, I think so.

Looks are one of the things that are taken into consideration in a relationship, that obvious.

But in some relationships, looks are a very big deal... In others (perhaps where the chemistry and bond is stronger), then things work because of a connection on a "deeper" level, and looks aren't as important then.

If an individual places a lot of importance on looks though, when someone he or she perceives to be much more attractive comes along, it may seem very daunting, or even trigger feelings of insecurity in this person.

Building a relationship when these feelings of inadequacy or intimidation exist may be difficult or even impossible, and this is why I think, it some people's eyes, there is such a thing as being too good looking for someone.

It's all based on a fear of being rejected, dumped, or left heartbroken I guess...

Yes I reckon there is a such thing as ‘ too goodlooking ‘
depending on the person , usually we do sometimes compare ourselves to other people , eg. Like you see some model you reckon if perfect and you see yourself as less .. Which you aren’t , but some people think of themselves as maybe , ‘ ugly ‘ or ‘ not decent ‘  or ‘ average’ and they may see some model and wonder , ‘ they tooo goodlooking ‘ , from your  perspective , like for example you see a guy and you may have a crush on him because hes  really goodlooking or great personality or whatever and you think you can never be with that person because they are too ‘ goodlooking ‘ for you , and thinking you don’t deserve that good , but that’s untrue
. Physical outside appearance doesn’t mean you are too good or low for someone ,but sometimes we label people as ugly , out of our league , not for us etc. And we also think we aren’t good enough , as ‘ perks of a wallflower says ‘ we accept the love we think we deserve’ ...