I don't believe that it'd really help. InnoDB will write to disk faster,however MyISAM will read from the database faster (which is the majority of your traffic). InnoDB will also restrict your searches to no longer support full-text searches.
We have been having problems with excessive accesses for a while. I finally got fed up with it and setup firewalld. I'm now blocking a number of networks.
A Content Delivery Network such as
Cloudflare would automatically mitigate most problems and give you the ability to block entire countries with just a few clicks.