Exarion Universe was absent toward most of the Spring/Summer 2005 Goat Format and was released during the very tail end for players who were able to get an early copy of it. It was never really tested during that format. During SJC Boston (2005), some player used a copy of it to round out their monster lineup. However, in modern Goat play, the extent of its dominance was realized. After the 2014 Goat Format tournament organized by the Yugioh community, it was determined that Exarion Universe did more harm to the game than good. And, as you can see on Duelingbook, it’s generally not allowed in most Goat matches.
It is a very well-rounded card. 1800 ATK and 1900 DEF. DARK for BLS Envoy and Chaos Sorcerer. Tramples against Goats. The problem wasn’t that one aspect of it was extremely broken. Tribe-Infecting Virus, for example, has an an amazing effect, but also has weaknesses: discard cost, WATER attribute, killed by Tsukuyomi. Exarion’s problem was that it had no unique weaknesses.
It also made too many cards in the format weaker or entirely obsolete, reducing the variety in deck building.
Skilled Dark Magician / Skilled White Magician – These were the LV4 Chaos-fuel monsters with the best stats, but Exarion sports slightly better stats and has an effect.
Enraged Battle Ox / King Tiger Wanghu – These cards punish Goats and other weak monsters but they’re EARTH attribute makes them hard to fit into Chaos decks (and their low DEF allows them to be exploited).
Gravekeeper’s Spy – Exarion is better as a defense wall because it doesn’t lock the player into holding a defense setup. Also, Spy gets punished by Nobleman, has negative Synergy with Goats and risks consistency issues.
Spirit Reaper – As a DARK monster (that’s also a defense wall) both cards are in direct competition, and to make matters worse, Exarion punishes Reaper with piercing.
Asura Priest – With Exarion in the format, Asura’s 1700 ATK isn’t as respectable. Exarion promoting more field pressure also means that Asura’s return to hand effect makes the player weaker to an aggressive assault. And on top of it, both cards exist for punishing Goats, so both are in direct competition.
Blade Knight – It’s just not safe for it to attack into an Exarion and then get destroyed by it next turn.
Dekoichi the Battlechanted Locomotive – It’s relatively strong stats for a Flip Effect no longer matter.
Kycoo the Ghost Destroyer – Players who ran it swapped it out for Exarion because it had the same ATK but was better in more situations, and was impossible to easily exploit.
Scapegoat – This card defined the slower tempo of the format, but with Exarion out, many players had to cut their Goat count to 2 or 1 (perhaps in favor of a Sakuretsu Armor). Scapegoat already had Airknight Parshath and Tribe-Infecting Virus to counter it, apart from just attacking the tokens in general. But Exarion perhaps crossed a line in making one of the most respectable cards into a somewhat optional card.
The ability for the player to run 3 Exarion’s was the inherent problem. Most aggro/Zoo builds ran 3, though even standard Goat builds (like Perovic’s) ran 2. Nonetheless, the player has to construct their entire deck around the possibility of facing a player who is running a playset. Perhaps Exarion Universe could have been tolerable at 1 (rather than 3) because it is not inherently broken; it could have been a “use it wisely” card like Breaker or Tribe. However, the argument that it’s release date was dubious is an easier sell than proposing an unofficial ban list edit. And the idea of adding another staple to further reduce the variation between decks is questionable.