No you are not "missing a trick" as even seasoned campaigners have trouble sifting the "good stuff" from the "not so good stuff".
As to people "dumping anything they like" - in a nutshell, yes. All registered Trainz users can upload anything they like as long as it meets the technical requirements for the type of asset, the version or Trainz build number, and is free of content errors. But that says nothing about the quality - only you can be the judge of that and not all users have the same views.
Unfortunately, a fair bit of that dumping is from Android users who use the DLS to store their unfinished routes.
Despite the issues of finding stuff, the FCT does have value. Those who do not have it often complain about the download limit and lower speeds they have to endure.
Some tricks I use:-
If the asset does not have a clear thumbnail image (and the message "This is Not a Thumbnail" does not count) then I don't bother downloading it. If you are going to put your time and efforts into making a decent asset then a minute or two to create a clear and accurate thumbnail image of the asset is not a burden.
If the asset does not have a clear description of what it is then "ditto", I don't bother selecting it.
If the asset is a small scenery item and has a huge file size (e.g. 10+ MB) then I am immediately suspicious. It was possibly created in SketchUp and comes with an enormous polygon count and hundreds of textures that can easily slow your frame rate to the level of a really boring PowerPoint presentation. The worst I can recall was a suitcase that was a whopping 50MB - it must have contained the Crown Jewels.
You can use the Trainz build number value as a rough guide. The lower the build number the older the asset and the less likely it is to conform to the latest standards but there are always exceptions. Here is a list of
Trainz build numbers and their corresponding minimum Trainz versions.