It's not such a direct upgrade since you're missing out on Chaos Magic. It's only a direct upgrade in content where Chaos Magic is not needed or is, at the very least, non-essential.

But, in content that requires Chaos Magic(*) AND you want to run a healer Soul, then you're either running Andromeda with Chaos Magic or Cass with an Ex ability. One such Ex ability could be Dartagnan's -20% Atk -20% Def. Oh look, not only does that -20% Atk make the lesser heal roughly equal to Andromeda's heal (and this going from 0% reduction to -20%, it's even greater going from -30% to -50%) but it also makes you deal more damage, lessening the amount of heals you need to begin with.

And even if you run double healer and the other one gets nailed, chances are high that her heals are on CD when she dies. And again, when that happens, ressing doesn't do anything. She'll just die when she gets back to the front before her CDs are off.

Fuck Andromeda. Seriously. Just run Cass for Healer type Soul. At least, don't even think about getting Andromeda until you have Arthur, Mordred and Dartagnan. This route also gives you Cass and Gawain (for the A type Def debuff, incase your KH covers B type), giving you almost all utility and versatility you'll ever need. Roland/Joan is missing, and considering how amazing they can be, I'd say they take priority over Andromeda as well. Oh, and I suppose one could consider Sieg as utility, but... well, by the time you're done with the basics (which I'd say absolutely does not include Andromeda), you'll be able to tell whether or not Sieg will be useful to you or not.

(*) Content that requires Chaos Magic equals EVERY fucking event these days? My god the devs fucking love their +100% Def up buff these days. And would you look at that, Yatagarasu is yet another fight with +100% Def buff. Wow. Thanks devs. That's really a lot of fun. Oh, and please stop with the +100% (or more) damage buffs too. At least Ygg was nice with the stacking +50% buff. More like that would be appreciated.