Its unlikely that youll even play Gush in the early game, as your lands will be best spent tapping for mana each turn
The presence of reach (this creature can block creatures with flying) alone demonstrates the strength of flying: How many other mechanics have a rival mechanic to combat them

Abomination, Terrifying Titan Agatha of the Vile Cauldron Amarant Coral Arbalest Engineers Arlinn, Embraced by the Moon Arlinn, the Moon's Fury Ashroot Animist Atalan Jackal Atarka, World Render Blitz Hellion Boartusk Liege Boom Scholar Borborygmos Borborygmos Enraged Borys, the Spider Rider Bumi, Unleashed Cactusfolk Sureshot Charging War Boar Collision // Colossus Collision // Colossus Colossal Might Deus of Calamity Domri Rade Domri's Nodorog Domri, Chaos Bringer Domri, City Smasher Doors of Durin Dragonborn Champion Dragonlord Atarka Earth Rumble Wrestlers Etali, Primal Sickness Fanatic of Xenagos Frenzied Arynx Furious Spinesplitter Gangly Stompling Gert and Old Lace, Runaways Ghor-Clan Rampager Giant Solifuge Gladiolus Amicitia Grove Rumbler Gruul Spellbreaker Hallar, the Firefletcher Hellkite Hatchling Herald of Ilharg Hugs, Grisly Guardian Hulk, Gamma Goliath Hustle // Bustle Junkblade Bruiser Khenra Charioteer Kogla and Yidaro Mina and Denn, Wildborn Minsc & Boo, Timeless Heroes Owen Grady, Raptor Trainer Polis Crusher Proud Wildbonder Quartzwood Crasher Raggadragga, Goreguts Boss Raging Swordtooth Rampaging Geoderm Raph & Mikey, Troublemakers Ravager of the Fells Red XIII, Proud Warrior Regisaur Alpha Relentless Hunter Rhino, Barreling Brute Runes of the Deus Sarinth Greatwurm Savage Packmate Scab-Clan Mauler Scarlet Spider, Ben Reilly Scuzzback Marauders Shivan Wurm

So the decrease in power-level in terms of damage is more than made up for by the ease of setting them up
Rarity Common, uncommon, rare, holo, reverse holo, full art, secret rare, etc