This user disagrees.
> Gmail is not encrypted
Don't know where you heard that but Gmail uses client-side encryption too: https://support.google.com/mail/answer/13317990?hl=en
They also use all the industry-standard encryption for requests. Proton may use different encryption techniques than Gmail, and because Proton doesn't run an ad business on my inbox like Google does, there are probably generally less crawlers in Proton messages than in Gmail, but wouldn't that make Proton faster?
I'm surprised the several seconds long splash screen doesn't get reported often - it's glaringly the only thing wrong with the service.