It is weird the difference between Windows Defender and Malware protection engine between 7 and 10 - AFAIK they are largely very similar in terms of protection yet on 7 updating takes ~1% CPU with a couple of flutters to 14% and rarely does much in the background with a few bursts to around 7% now and again in response to doing stuff with files, etc. Windows 10 updating it often sits there using 20% CPU, etc. and will frequently ramp up to 40-70%, if it thinks the system is idle/and or whenever it feels like it will sit there using 20-40% for 30-40 minutes at a time not infrequently, etc. - complete clown show at MS.