"Cascade was fucking stupid. It is so fucking stupid I cannot imagine a reasonable designer playing Magic and going “hmm yes well this mechanic is rather magical” and not “this mechanic is fucking stupid.” Designers might not be the ones that have to decide exactly what mana cost and power/toughness something ends up as, but they should be able to playtest, say, a three-mana 2/2 with your new mechanic and go, “this mechanic is fucking stupid.” [1]
[1]It wasn’t in Shards, but Planechase did print a gold three-mana 2/2 with no other abilities. It defined a Legacy deck for a period of time.
Cascade is inherently incredibly powerful: you get something that could cost only one mana less than the spell you played, so if you hit a spell that costs that, any non-cascade parts of the card only cost one additional mana. This probably means that you would get, say, a vanilla 2/1. Instead, Alara Reborn gave you a 3/2 with haste. That’s so beyond what it should be that it’s just not in the same stratosphere. That’s on the developers, obviously, but I blame the designers, too. They created a mechanic that inherently could not be balanced. And how do the designers respond to this? They basically tell people that we’re wrong, and it is a good mechanic. Nope, sorry."