Mid 8 Man Setup - Why the hate on Thanes, BD, SM?

I don't know which time zone you are playing in, but during EU PT, literally every mid /gvg group is a hybrid with RM+BD. RM+SM is less popular due to the missing interupt capability of the BD, but you see this setup from time to time. Full caster groups are doable, but difficult to coordinate, as you often have to push with three casters, two of them with inferior range, on 4+ alb caster groups.
Thanes, well that is a problemaric case. In general Thanes are seen as worse warriors in terms of the peels slot, because they lack stoicism, DD, SB and dps/defense qualities of a 50/50 hammer/shield warrior. We ran a Thane from time to time in our group, but mostly only if we couldn't find an adequate replacement for our warrior. They are sometimes included in full tank groups instead of a RM, rupting together with the skald and offering a second slam to the group, freeing the warrior to peel, but you rarely see this comps running, because hybrid setups are the meta right now and vs. the famous 4+ alb caster groups, NS is very valuable. If you include a RM, want the defensive RA's of the Warrior and a Thane, you can only include one Zerker/Savage, resulting in a group with limited dps, even if your melees are high RR.
But despite those reasons, I agree with you that trying something off-meta sometimes leads to interesting and rewarding comps, and if you take your time to try out those things, you may even have fun while doing so.