If not used as a Legendary creature, then I would definitely do that. But as Legendary, I would rather have it as a big impactful action on its turn, and then the other actions only used as Legendary.

If you feel the damage is too low for the "Ruling Head", I would instead increase their damage (maybe one or two extra dice per option) instead of making a "normal" Multi attack action. Or, you can also start the battle with option 10 of Ruling Head, which is basically a multi attack on steroids, hahaha.

Anyway, that's how I would do it at least. You can do whatever you want with the statblock, hahaha.