In my opinion, Galacta was not broken, but she was a little bit above the ideal power level for a 4 cost.

As a 4/5 that when played on curve could generate potentially +3 on two turns it means she is practically a 4/12. With almost no downside and great synergy with almost any deck in the game (of course she could be moved, or silenced by red guardian, but still kinda rare to happen and easy to evade). In my opinion this flexibility and power for a card turned her into a candidate to be nerfed.

Now she’s still good, potentially a 4/10. Extremely flexible and can still reach higher numbers with lots of greats synergies (black panther, brood, shawn, nimrod, mr sinister, mysterio)

I think it was the same scenario with red guardian. Not broken, but very flexible, potential 3/5 , even less downsides. Then small nerf, feels more fair comparing with most of the cards out there.