I got to pro ladder with the deck below, the final 3 folks I played against were playing meta decks and forfeited. I can't claim its the best deck ever but it definitely has some tricks up its sleeve.
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I think the best way to buff harmony would be to give more of the underwhelming ST cards the harmony tag. That way you have more benefits from playing the archetype and a moderate buff to some cards that could use some love.
The way that Harmony interacts with neutral cards is also pretty frustrating, mainly that playing a neutral card before the ST card with the same tag will prevent the Harmony proc from activating once the ST unit is played (so playing a bomb heaver before pavko prevents pavkos harmony proc.) I can see a few ways around this but none of them are perfect:
Let harmony work with neutral cards and card tags. This could totally break the archetype and force players to play super weird neutrals just to get harmony procs but its worth considering.
Let harmony proc more than once with the ST tags but just not for units that share the same tag - this would mean if you have a half elf hunter it would proc for every non-elf unit even if it wasn't on the board. This might also break things but it would at least bring it closer to how comparable mechanics like assimilate or thrive work.
Prevent neutral cards from obstructing harmony - this is the least interesting but changes the least about how the mechanic works.
I have a soft spot for harmony and ST in general so I'd like to see it get some love but I also recognise that there are higher priorities for balancing and ST is probably one of the factions that can compete with the widest varieties of playable decks right now.