From my own testing at 503 ilvl I get a 10-15% ish dps increase single target with the lei-shen trinket as Demo (service, with and without EA glyph), while it having no noticable advantage over other trinkets for Aff and Destro (moonwell chalice all over again). Obviously things change after having aquired better gear, but it feels surprising Aff would be able to both catch up and beat Demo in this tier single target, the meta gem would have to be that much absurdly better for Aff (do we know the average proc rate? This new ppm system seems really unreliable)
As reference point:
From my own testing without the lei-shen trinket the three specs all performed similarly (within a 5% variance) on single target.