This started from the premise of definitely using Mega Dragonite, a Pokémon the builder is very attached to, and fixed a Ghost/Steel-type Pokémon as the first partner, since it covers each other's weaknesses (Fairy/Ice vs. Ground/Fire) and even nullifies the opponent's Fighting-type moves. After that, the final six were completed by swapping in whatever tech pick was trending at the time — for example, using Mimikyu as the answer to Rain teams, or replacing the Fighting-type Mega with a Steel-type Mega.
Dragonite is run as a special attacker, but for consistency it uses a repeatable, 100%-accuracy Dragon-type move rather than a riskier alternative; its in-team selection rate is overwhelmingly No. 1, and it's brought out first in nearly every match. The Water-type helper is a card carried over from the previous season that takes hits from many Speed-based special attackers, the newly joined Ice-type cleans up opponents that lack a Speed advantage with its priority move, and the Steel-type Mega checks the Fairy/Ice/Fighting group.