Good question, I think should be that locks can use summon like solo spel without any help, and maybe assist other 2 ppl just makes that can summon by one step some group of ppl. For example, mages can open portals without anybody help for towns and other group members can use too.
It will be nice if Blizz think about redesign this spell.
The Ritual of Summoning mechanic is basically a relic of the past. However, I think the rules are fine as is.
If you could do it on your own, it would feel like less of a ritual, plus you still need help from someone else for the actual summoning.
If you can do it with 1 person helping, nothing much would change, though it would make it possible to more easily “cheat” in dungeon runs. The effects would be fairly contained though, as the warlock would still need to be useful outside the summoning/skipping bit.
So, all in all, it’s a spell with very few drawbacks, and the requirements that are in place remain fair enough.