Not exactly. Maybe you benefit from an additional virus scan (if Proton does this).
What you certainly benefit from is the "only load external resources when told to" feature. This prevents tracking since loading the external resource == the mail was opened.
What exactly do you want to achieve in terms of security?
IMO people mainly just want big tech to quit snooping on everything they do.
On the other hand, it is a lot of hoops and a large learning curve for those to whom have no idea where to start other than having big tech stop snooping.
The problem with a late stage capitalist world is that the moment you realize you want to escape Big Tech, there are already numerous of services selling pseudo or marketable privacy-respecting product with comparable convenience to the competing Big Tech counterpart. This appeal to non-technical consumers means their willingness to "vote" with their wallet what they thinks is the best replacement.
The drawback of this, for non-technical consumers, is that it's hard to distinguish between no-nonsense actual privacy-respecting services (with caveats laid out before you pay), where you're forced to do research, and those filled with buzzwords and marketable features, where it's easy to completely put your trust in these companies.
By definition, if you don't feel like putting in the homework, you are ceding control to someone else. At that point, all bets are off. Even trustworthy entities can turn on a dime. Ease and full control are mutually exclusive.
Get your own domain and use that with Proton so you can take your email address to whatever email provider you want, or host your own. In the future, switching won't be nearly as hard since you'll just need to redirect the domain to the new email provider instead of changing your email address with everyone, again.