even I dont like it that much compared to playing decks preassembled for me
Of course, there have been cases in which it was done simply for the sake of doing it, but it was quickly found out those cards didnt do much for the game as they are quite situational, so the newer iterations were either pushed or R&D tried to do something more interesting with them

Synthoids Abdel Adrian, Gorion's Ward Ad Nauseam Adaptive Sporesinger Adventurer's Airship Aerial Formation Aetherborn Marauder Aetherflux Conduit Aethersphere Harvester Aetherwing, Golden-Scale Flagship Agadeem's Awakening Agent Frank Horrigan Air Response Unit Ajani's Presence Ajani, Outland Chaperone Alacrian Jaguar Amethyst Dragon Amethyst Dragon Aminatou, Veil Piercer Ancestral Knowledge Ancient Brass Dragon Angel of Salvation Angelic Aberration Another Round Ao, the Dawn Sky Apex Hawks Apocalypse Runner Appa, Steadfast Guardian April O'Neil, Kunoichi Trainee Aradara Express Arc Lightning Arc Mage Arcane Bombardment Arco-Flagellant Ardenn, Intrepid Archaeologist Armed and Armored Armory Automaton Arrow Volley Trap Arsenal Thresher Artisan's Sorrow Atlantis Attacks Atomize Atraxa, Praetors' Voice Augury Owl Augusta, Dean of Order Aurelia's Fury Aurora Awakener Autarch Mammoth Automatic Librarian Avacyn's Judgment Avatar of Hope Awaken the Blood Avatar Ayesha Tanaka, Armorer Balamb Garden, Airborne Ballista Charger Baron Helmut Zemo Barrel Down Sokenzan Batroc the Leaper Battalion Foot Soldier Battle for Bretagard Battlefield Improvisation Beast Mode Beatrix, Loyal General Berserker's Frenzy Bespoke Battlewagon Bessie, the Doctor's Roadster Better Than One Biblioplex Kraken Big Wheel Bilbo, Birthday Celebrant Bioshift Black Mana Battery

Or vice-versa
This isn't as good as giving the creature +5/+5, but it's still a boost to smaller, early-turn creatures