Additionally, Radware only handles packets if the Proton mail service is under attack, plus those packets do not get routed to Israel, but to Frankfurt/Germany.
On the other hand, email in general usually is an unsafe medium. You can logon to Protonmail via https so no one can see your password, but when you send an email to another email server, this server may not be able to encrypt the mail and therefore the mail is readable by anyone who has access to the traffic.