The point of trading card games is the convenience of being able to play anywhere
If you were to have a land type count as that color instead, you would allow Mtenda Lions and such, but disallow many more things
The problem is having to rely on having the land in hand for this to work
(6/6/2025) If you put an Aura on an opponent's permanent, you still control the Aura, and mana symbols in its mana cost count towards your devotion
Mana Vault Description : Mana Vault is an artifact that taps for three colourless mana, but it comes into play tapped and requires paying four mana during each upkeep or untap step, or else it deals one damage to its controller
Its easy to get caught up in the hype: a card spikes, everyones talking about grading it, and before you know it youve spent more on submissions than the cards are worth