For this not to be a PR shield (i.e. for Israel to really be able to read protonmail) the link would have to be an outright lie, or protonmail would have to have shared key data.

Heck, even if somehow radware (the BGP-based DDoS proxy they use) had access to protonmails private key or had minted their own SSL cert for protonmail, you'd still be protected by PGP.

For outgoing mail, they don't use radware so even if you were to send plaintext emails to a mailserver that doesn't support SSL encryption, radware still wouldn't be able to read that.

Unless the linked statement is just a lie, their DDoS protection service is not able to MitM them. Your proposed scheme seems a lot more convoluted than protonmail just giving access to the Israeli government. Similarly, it seems a lot more conspicuous.

If you don't want to use them because it indirectly supports an Israeli company, that makes sense, but their DDoS prevention scheme as outlined does not harm privacy in any way.