>>26656742in VGC15 (that pic is from Worlds15), the genies were extremely good pokemon. Landorus can provide intimidate support (which was invaluable in a meta with M-Kang), has pretty decent bulk, meaning it can stand most non-ice attacks, had a nice movepool and was pretty strong against other common pokemon, also the scarf set with rock slide became infuriating since the flinch chance is pretty high. Thundurus had prankster T Wave which on it's own is great, and also had good stats and typing, making bulky variants difficult to knock out while dealing decent damage; there was also the possibility of priority swagger, which not only is pretty powerful, alongside T-Wave and Lando's Rockslide made games RNG-heavy, which is very cancerous.
The mons themselves weren't broken by any means, but when you also have things like M-Kangaskhan, Heatran, Cresselia, etc, you can have a team of 6 pokemon that are just very good on their own and also pair up incredibly well, which resulted in those pokemon becoming boringly overused. In Worlds top 8, 6 of the 8 players had some variation of the same team, and all 8 players had Landorus-T.