google – Do I receive DDOS crawlers?

My website is currently hit by spam bots (example: 66.249.73. *) That result in heavy CPU usage. Is it common for Google / Bing to explore a 10 / sec website?

I have done reverse lookups on IP addresses and they appear to be valid crawlers using https://support.google.com/webmasters/answer/80553?hl=en.

As I have blocked some IP addresses, the Google / Bing search console reports errors and hurts my index.

It happened this month (April). Is this a referral attack? Is it possible that someone is usurping IP addresses? Can I do something to limit the number of scans?

I'm currently creating a server-side rendering for crawlers, but it's a tedious task for something that starts to happen randomly.

Thank you,