Gavi is to some extent an exception to this rule
Or, you know, turn a green mana into 3 of another color entirely
Then, anytime you cast another colorless spell with Ugin in play, you'll exile another permanent that is one or more colors
This card is fairly high on the list on the Japanese side in Terastal Festival ex as well, but the fact that our other potential Eevee SIR was turned into a promo instead means there is a lot more focus on this card in English
So, Gruul Spellbreaker could be a 4/4, or it can swing right away as a 3/3
That doesn't mean I haven't had to sit my son down a couple of times to review what is (and is not) appropriate, but I would rather they filter themselves than relying on a 3rd party to limit my kids' speech