In LE, unlike in PoE (especially PoE2), taking +skills isn’t the be all end all. In many cases, like we’ve explained, you’re better off not them and using another affix instead.
Yes, wraiths have more nodes that will become less useful if you build them one way rather than another. That is because wraiths actually give you lots of options in how to construct your skill. Skeletons don’t.
So the fault isn’t in wraiths. It’s in skeletons. There’s a reason why you have so many wraith based builds and very very little skeleton (other than skeleton mage, which is another skill) ones.
The skill trees are made in a way that you can build around them and +skills will benefit them a lot. But if it’s not your main skill, then +skills usually don’t.
As I said, wraithlord or flame turrets both use lots of +skills for summon wraith. They’re not wasted.
But your build isn’t created around wraiths, so +skills will get less benefit the more you have. You’re better off with another affix instead.
And, to go back to the OP, all of your examples give you more damage. Not much, but some. Which is a lot different from reducing your damage or ruining your build.
As for your wraiths, if you have +10, you could still get a lot of decent or even good nodes:
-Putrid wraiths at the bottom seems like an immediate win on a poison build.
-If you “pay the tax” following the necrotic nodes, you get access to more movement speed and +wraiths.
-You might not care about crit, but if you go to the left and take the higher crit chance, it will also heal them on crit, so it will help with their survivability.
-And lastly, as pointed before, on the top you can summon more than one at once, which can be very handy when your party gets wiped by an AoE.
So you still have options. You just don’t like them as much.
Which, again, is a clear sign that, for your build, you’d be better off with another affix.
Finally, I’ll just leave you with an example of a build that has +8 to wraith and could still use more:
https://www.lastepochtools.com/build-guides/keepers-wraithlord-necromancer