You could do SL premium (3/month), Pass+ (2.99/month), and Drive+ (200GB 3.99/month) for $9.98/month. Just saved you 12 cents. 
Seriously though, the real savings is that its much easier to just make a new account with the same service each year, if each service is tied to a separate account.
This means you can take advantage of the Black Friday deals every year. That’s a ~20%+ saving every year vs 1 year of black Friday savings with an unlimited account. This is mostly because Proton cares more about “new” customers then existing customers.