This is how beta software works (not just at Apple). When updates come out, it's very normal for some things to get better and some to get worse, especially when adding new features. Not every beta is focused on optimizing all parts of the operating system. They're meant to test different features/code for new enhancements.
We accept glitches and stutters here and there. However it is necessary to keep an overall interface consistency and keep performance at a relative level. That doesn't mean each beta, performance must improve, but at least, don't drop too fast to let testers notice it with no effort. Battery life is the same. I think few testers will say "my phone can use only 10 hrs after installing this beta. Before that I could use 12 hrs. This is not acceptable". But if battery life is halved, or even worse, this is a real problem.
Obviously, beta software is for TEST propose and should not be used as daily drive. But if performance and battery life drops and rises like roller coaster, this would not be good.
Sorry for such messed comments.