There are two aspects to this - antibodies and white blood cells - T-cells and B-cells. Yes, the antibodies fade in a few months. The T and B cells don't. That's why they say that you still get protection from more severe disease.

We have a "perfect is the enemy of good" here. No, the vaccines aren't perfect. But they are pretty good, they do help, particularly so it's not so bad if you do get it. The find point is that just because they're not perfect doesn't mean they're completely useless, because they're not.

I'm over 65, I've gotten all of my shots on-schedule, and I still mask when going indoors into "public air" like supermarkets, and such.