Neutral sothe worth it?

I would suggest doing so. Even wish neutral stats, he reaches 55 attack with Peshkatz and Life and Death, and 41 speed with Life and Death and Speed +3.

Short answer: yes

Long anwer: depends on you.....

Like if you get a "perfect" iv one later one. Youll be faced with the question of merging and foregoing a perfectly good LnD fodder or fodering off the neutral one to use the other one and foregoing all the investment you put in him.That is the real question here that only you can answer tbh.....

I would rather not, Sothe is great unit and all, but you should prmomote +spd or atk one in my opinion. If you will merge him later, you don't care about serching for optimal ivs as much.

Fodder

If you really need a dagger unit, he's one of the best. But if you're not in a hurry, wait for a +Atk or +Spd one to maximise his potential.
I have a +Atk -Def one that I use all the time.