I am a non-meta scout c3 build. I really can't perform well in grinding, et, 315 dun, solo mission etc etc etc. But, I like my scout. I guess the reason why I still play tos is because of how I like scout's playstyle.
Yes, I have seen many non-meta classes at high levels. Many people who are non-meta (or semi-meta) builds are always rerolling characters as they like to try new builds.
Overall, non-meta builds are meant to be fun. Party grinding usually just need a meta aoe (with good dps) and a good healer, the rest usually are fillers. Most grind parties are kind to non-meta build, unless they can't clear effectively. The 3 main situations I think non-meta builds are punished heavily are end-game pve contents and boss hunting. Pvp-wise is much more flexible. There can be many slight variations to a pvp build. For example pvp inquisitor build has many variations such as diev-based, priest-based, into druid, oracle or kabb etc.
ps: (non-meta pve builds does not mean anything goes. It still have to be a workable build in pve)