Dracovish and Dracozolt may have the same stats, but Dracovish is still miles better.
Dracovish only has 2 weaknesses (Dragon, Fairy) due to it's decent Water/Dragon typing. Unfortunately, it only has 2 resistances to Water and Fire. Dracozolt, on the other hand, has 4 weaknesses, those being Ice, Ground, Dragon, and Fairy. It does have 6 resistances though.
Dracovish and Dracozolt have different movepools, obviously. I don't know what you mean by a "better movepool," on Dracozolt, because it doesn't have as many coverage moves, and the ones it does have are usually inaccurate. Especially with it's bad ability, but we'll get to that later.
Notable moves for Dracozolt are: are Aerial Ace, Bolt Beak, Breaking Swipe, Dragon Claw, Earthquake, Stone Edge, and Low Kick.
Notable moves for Dracovish are: Crunch, Fishous Rend, Earthquake, Leech Life, Iron Head, Zen Headbutt, Low Kick, Stone Edge, and Psychic Fangs. As you can see, Dracovish has the Serperior learnset here.
Dracozolt's abilities are Volt Absorb, Hustle, and Sand Rush (HA).
Dracovish's abilities are Water Absorb, Strong Jaw, and Sand Rush (HA).
Dracozolt has very mediocre abilities. Sure it has an immunity to Electric, but it double-resists that anyway. Hustle sacrifices accuracy for power, making already inaccurate moves like Stone Edge or Fire Blast unusable, and making other normally strong and dependable moves like Earthquake just a little bit less likely to save you when you need it. Sand Rush has no usefulness other than on Sand teams.
Two of Dracovish's abilities aren't much better. Water Absorb gives another double-resisted immunity, and Sand Rush is only useful on Sand Teams. But oh boy did it get another amazing ability. Strong Jaw boosts the power of biting moves by 1.5x. And Fishous Rend is a classified as a biting move. Yeah. It's pretty powerful. Add STAB and maybe a Choice Band or Scarf, and you'll be OHKOing with even resisted hits. Strong Jaw also boosts a lot of other moves Dracovish gets.
I was talking about singles mostly, but apparently Dracozolt gets more usage in Doubles, because of Dynamax moves not missing. It can then abuse Hustle, basically getting a free boost with no drawbacks. Max Lighting sets up Electric terrain, powering up Bolt Beak, and Max Airstream raises Speed, making it more likely that Dracozolt will outspeed and have Bolt Beak's power doubled. Dracovish usually doesn't Dynamax, and usually relies upon a Choice Band/Scarf.
"In series 6, Dracozolt has a usage percent of 18.3%, and While Dracovish only 8.86%."
(Thanks to ~MegaCharizardY~ for the information in the Doubles section!)
Here's movesets for both of them though.
Dracovish @ Choice Band
Ability: Strong Jaw
EVs: 252 At and Spe, 4 SpD
(I got Dracozolt's set from Smogon)
Dracozolt @ Choice Band
EVs: 252 At and Spe, 4 HP
-Fire Fang/Aerial Ace