ProtonMail focus on security and paid services, free tier is almost useless. Gmail is free service that make money on pushing adds and selling your privacy but provide excellent service. There is no conflict of interest.
SEO it is hard to say. They want to compete on "email" and "secure email" keywords it is not going be easy.
Can you elaborate how free tier is almost useless? I'm using ProtonMail as my secondary e-mail and I'm on free tier, and it is pretty useful. Much more useful than FastMail which pretty much forced me to switch to paid plan right away or else I will be unable to send e-mail - all this to combat spammers.
> G Suite Email is a paid service that doesn't sell your privacy
G Suite is an american service and will give away your privacy without a proper/open court case when receiving a gag order. This is very much in contrary to PM.
SEO it is hard to say. They want to compete on "email" and "secure email" keywords it is not going be easy.