No. That could just be standard heat throttling, OS variance, or background tasks. Not to worry.
It's a shame Apple can't be trusted anymore. Hopefully with the new OS update they will explicitly say "we slowed your CPU down because your battery sucks," or hopefully in the future, they will have better or larger batteries to minimize or delay throttling, or design their chips to not draw so much lower.
I'm okay with Apple throttling because they have to, though I wish they can design it to be avoided. What I'm not okay with is Apple not saying it cut performance by half and telling me my battery is fine. They never once said a battery can improve performance- they wanted us to upgrade.