Legacy and Vintage are great formats, and most players would be perfectly fine with playing against opponents with some number of proxies in their decks if it meant they could play their favorite format on a regular basis
Some of them were so compelling and popular that they formed the foundation for future card designs in tournament-legal sets
This creature's controller and that player each draw half that many cards, rounded down." Preventing player damage (or damage to your MTG Commander) is a pretty powerful play, especially when the only cost is allowing you and your opponent to both draw cards
It gets to keep all the special abilities and effects they have though, letting you have extra copies of them out and about
What does have predictability are the factory-sealed preconstructed decks
While it may seem mild at a +1/+1 counter, a 1/1 creature, or 2 life, these add up fast