I have nothing against Proton or any of their products, but I took the opportunity of switching away from big tech to also switch away from the all-services-in-one-provider model. Moving everything from let's say Google to let's say Proton just kicks the problem down the road. If Proton ever goes evil or goes out of business you're now looking for a new home for all your services again.

Its also generally good privacy practice to use a VPN provider that is wholly separate from any other provider you use so that provider can't relate your VPN traffic to all the other data they have on you. This is more true from providers who aren't trustworthy, but it's a rule I follow regardless.

Of course, this all depends on your threat model.