Hi. I didnt read the entire thread so sorry if i repeat things that have been said already.

First of all as you said, souls strength change depending on the content you're doing (raid / event / daylies)

I'm a main Siegfried and i'm really happy with her, but on daylies she is just an auto-attack bot and you would better go with Granuaile or profit to lvl up other heroes.
But when it comes to boss with rage / stun mechanics it change completely. Event boss is just faceroll actually and she really deserves her "mvp stealer" tittle on raid boss as you can still gain mvp even if you came in after other people.

For Andromeda its not only a "if you need a healer" thingy. During a raid, her heals, as every other souls buff, will benefit
to other people in the raid, making her one of the most valuable hero. Not even talking about her rez to recover if you messed up.

Pretty much every heroes have buff like that, the only one who doesnt is Solomon.

Even in solo situation, i assume people talking about optimization here managed to get ssr, and its more interesting to have someone able to buff them than a damage dealer only.

You can say that its the same for Siegfried, the only credit you can give her is a better control on a raging boss, which is what Solomon does in a different way while being better in general situation, and you would be right. But if you aim for mvp Siegfried is a stronger pick, and you still have the choice to switch on the snatch-bot (believe in snatch \o/ ) on daylies.

In the end (for what it is worth considering i didnt play on dmm), i don't think there is any bad choice, and you should play the hero you enjoy the most.

ps : sorry for average english