At first, when Bitdefender is installed, it uses a bit of the CPU, even for adapting to the client's system. So, after this phase and especially after a complete system scan it tends to drop, to have an idea on my machine it is around 0% and 1% CPU utilization.
Don't want to bloat? Go ESET! For me, it's the only quality AV that actually has its OWN motor and has no bloat. In it, you won't find VPN, Password Manager, Parental Controls, browser extensions and all other types of bloatware. Besides, it's very light, it's always up-to-date, the updates are small, you start the system, and it updates itself, in short, several interesting features.