Spell Queller is able to disable a Vanguard even though Vanguards are not specifically named as something the effect can affect. The card text and card effect aren't consistent with each other and one of them should be updated.
Speller Queller (10) 2/3 Creature - Spirit
When this creature enters the battlefield: Disable the opposing card with the highest base cost.
When this creature dies: You may create a copy of a random opposing disabled nontoken card into play under your control.
Vanguard This card is Legendary. While it's on the board, it can't be affected by effects that don't specifically name Vanguards as targets. Vanguards have abilities that can be used once per turn, by tapping its gem and selecting an ability.
I think you're right but the card text should be fixed to include vanguards.
I don't really have a preference about if they change the effect or the text. Vanguards already sometimes confuse people when everything is working by the rules. Having a card that doesn't follow the rules makes it more confusing.