Nah, there's a lot of reasons why most low tiers are low besides lack of interest. Yoshi was a bit of an odd ball case, where he had tech that people thought it couldn't be used effectively. Amsa proved that was false, but that doesn't mean every character just needs an innovator to make them good. Some are just bad. For Young Link specifically, it goes beyond kills being hard to get, cause you could just have sick nasty edge guards and that problem wouldn't be that big a deal. Almost all of his safe approaches can get CC'd really well, and the only moves that don't get CC'd are laggy. He's also pretty light as well, but has high fall speed so he gets comboed pretty hard. His recovery isn't amazing, but it's not too bad. His grab is also pretty lame, and his OoS options aren't spectacular.
I personally think Young Link has a lot of room to grow, specifically around his projectile game (approaches and setups), but that doesn't necessarily mean he will be amazing. So I agree Young Link is hurt by lack of interest, but that isn't the case with all low tiers. Example: Roy. You think people don't want Roy to be good? Everyone would love Roy to be great, and many have tried to make him good. The necessary tools are just not there. If you have someone like M2K play Roy and hardly do well with the character, there is something wrong.
tl;dr: Young Link could use a lot more interest, but that's not why low tiers are low.