Electivire (+Flygon or other support) is still a decent deck, but it has autoloss against G&G/Plox, both because its fighting weakness and its dependance on powers. Since G&G is the most popular deck right now, Vire shouldn't be a good choice for a competivie tournament.
competitive tournament = State Championship or higher
I've won a Battle Road with an Exploud deck because I was lucky enough not to get paired against a Magmortar player. I also have won all matches in a league with a fun deck featuring Azelf/Uxie/Vesprit, Golduck and Octillery. Of course this is possible at smaller / more casual events and Pokémon would be a bad game if it wasn't.
But Golem, Donphan or Lucario don't help against G&G, and I still don't see this deck have a chance to win States/Regionals in Masters or Seniors (I also don't see any synergy between the cards you mentioned btw).
This should explain why you can win with this deck combination. ^^
(in Juniors there isn't a real metagame at some Battle Roads / City Championships etc, you should be really happy not to face a Gardevoir deck in every second match)