Yes, whatever other issues people have with vaccines or especially the politics around them, vaccines do reduce the chance of serious disease. They seem to be less effective than resistance gained through infection, but do protect against delta.
Yes I think this has enough data to support less severity of illness with Delta. And because you are still able to be socially functional with the reduced severity, on average, you'll be out and about spreading it and keeping it alive and changing. This will be an issue when your vaccine immunity wanes and perhaps they don't dial in the next version of the booster to match or get it to you in time
It also depends how many months have elapsed since your last shot, more than five and it seems to be waning in Israel.
With, mu early indications seem to point towards it not working to reduce severity.