The DPS shown there is on a neutral target. So neutral DPS with dragon moves is higher.
But if you are fighting a Kyogre for example that electric DPS is gonna go up, whilst the dragon DPS is gonna go down, because of the type matchup.
Zekroms electric neutral DPS is the highest out of all pokemon with acces to electric moves, thats why its the best electric type.
Compare its dragon moveset to other dragons and youll see that Rayquaza for example has a higher DPS (but actually lower TDO) so rayquaza is “stronger”.
Its actually pretty hard to say wich pokemon is the strongest and what is the best moveset, cause it all depends on what you are fighting. Sites like Pokebattler.com are a great help for raids, but its also weather and moveset of the pokemon youre fighting dependend so theres ALOT of different “bests”.
On average (extrem weather and unknown moveset) Palkia is the best pokemon to fight Zekrom in terms of shortmanning. But change the weather to sunny and suddenly Excadrill takes the top spot. Change the moveset and then its Garchomp or Landorus or a shadow salamence.
The differences are very small though. Against the worst matchup with Palkia you still only need 3 level 40 trainers (with best friend boost) to take Zekrom down. The only difference is about 15 revives per player.