In MTG, was there ever a five-color deck that worked well?
Yes. Emphatically yes.

Some notable examples include:

"The Deck" by Brian Weissman – a classic five-color control deck focused on reactive play and denial with only Serra Angel and Braingeyser as finishers; arguably the prototype for all control decks, and the strongest Magic deck of its day.

Jakub Slemr's 5-Color Black Weenie deck — a black-based creature aggro deck using cards of all five colors for efficient answers and disruption (and sheer card value from running most of Visions' good "ETB" creatures); 1997 World Champshiop winner.

Many Llorwyn-era Cruel Control decks, like this one — these were not as absolutely dominant as the previous examples, but Vivid lands made it reasonable to play even absurdly "greedy" combinations like putting Cloudthresher in the same deck as Cryptic Command and Cruel Ultimatum.

There are also numerous four-color decks that could possibly be adapted to a fifth color but don't really benefit from it much, especially in the modern day, when the Legacy/Vintage card pool is a lot deeper and "color pie" design conventions have changed a bit to make it easier to access certain effects without having to go into one specific color.



The reason you're stumbling is that pre-assembled multi-color decks tend to have garbage mana bases, because part of the game's business model is to force good multi-color supporting lands (which are highly desirable for a range of competitive decks) into rare/mythic slots, and preconstructed decks are limited to only including a handful of rares. On top of that, some styles of cards (like Moxes and no-drawbacks ABU dual lands) are considered too powerful to print today.

This answer discusses some of the benefits of four- and five- color decks, as well as tricks to their mana base construction, in more detail.