I had my Pixel 6a for about 4 & 1/2 months prior to installing GOS, so I have a bit of a reference point when comparing battery life of my phone prior to and after installing GOS.
GOS did increase my battery life enough that I noticed it in my daily usage. Obviously, how people use their phones will differ from person to person, but I argue that if one spent some time with their phone on stock Android for a bit before installing GOS, they would notice a difference afterwards.
I'm not trying to move you in a direction that you are uncomfortable moving into, but installing GOS is easy and safe (just make sure you follow the instructions on the official site [https://grapheneos.org/install/].
Heck, I installed GOS on my 6a using a laptop running Linux Mint (which is not an officially supported Linux distribution) using the Brave browser and had zero issues with it.
The devs have made GOS a super easy install, and they have great support team as well. It's understandable to weigh your options as you don't want to jump into something you're not quite sure about. It took me a little bit before I decided, but I'm very happy with my decision.
Cheers!