The closest I have been to that was in Ruby, where the only normal Pokémon I trained was my starter, Mudkip. Then I trained both pseudo legendaries (Salamence and Metagross) and some legendaries (Latios, Latias, Groudon and Rayquaza). That was nine years ago, though. I rarely use legendaries nowadays.
I once played through Pearl using only a team of 6 legendaries - Rayquaza, Moltres, Suicune, Groudon, Shaymin and Latios.
Just wanted to try something different, so I made up this totally random team and went with it.