Early on maybe not as important as other things, but sooner or later you'll find you have far more skill points than you actually need and at that point any passive which isn't totally irrelevant is worth getting. Or at least better than unlocking an active skill you'll never actually put in the limited space on your bar or leaving the skill points unused.
Except Soul Shatter, which requires you to have either Soul Trap or Soul Strike slotted to use, unless you're using either of those two there's no point unlocking it because it will never do anything.
PC EU player | She/her/hers | PAWS (Positively Against Wrip-off Stuff) - Say No to Crown Crates!
"Remember in this game we call life that no one said it's fair"
If you've got the extra skills points to spare, sure, pick up soul lock. Soul summons if you really don't have anything else to get.
Soul Trap and Soul Shatter is only worth it for that once-in-a-blue-moon update when Soul Trap is actually a meta DOT or Soul Strike is effective. Unless you just like those skills, in which case, go for it.
Some extra aoe damage below 20% may kill the boss or get you the kills under 5% health PVP achievement, but if you still have to think about where to invest your skilpoints, picking something that prevents you from getting that low on HP is a better choice. (also keep in mind you need to have soul trap or the ultimate sloted for this to work)
Saving one soul gem every 1 or 2 hours is meaningless. Either you die rarely, so saving one while collecting a dozen doesn't matter, or you die so often that using up one less is meaningless as well.
The passive soul trap was useful before they made the soul trap skill so attractive. If you don't use soul trap as a dot ability, then the last passive is useful, otherwise you will trap souls with every kill anyway.
As far as I can tell, Soul Strike and Soul Trap are in a good setting atm, soul summons is ok, shatter soul could use a rework since it is practically never used (if it didn’t require a soul magic ability being slotted, different story.), soul lock is fine at level 1, but at 2, definitely needs a rework since your wasting a skill point just to increase the proc Chance.
If you see me anywhere. Know that I am sitting back with a bag of popcorn, watching as ESO burns the goodwill of its player base with practices that only disrespects the players time like it did to me and many others...
If a game does not respect your time, best thing to do is move on from it and find something else.