Also hot take: I don't think running lots of +1/+1 counter support cards are good here
While that is true, playing several colors means that youll have to put extra effort into building your manabase if you want to be able to cast all your cards consistently
However, its hard to beat a card with three different abilities that all help your opponents in one way or another
Synergy with flickers and discard payoffs like Tinybones, Bauble Burglar, Entropic Battlecruiser and Waste Not, then backed up by counterspells and alternate plans like control, reanimator and wheels
However, if there are not creatures on the battlefield, then Tamiyo doesnt do a whole lot
Each card is still only legal in its previously eligible formats prior to its inclusion in the Mystical Archive