It's not necessarily cheaper depending on how often you'd like to upgrade. Upgrading to v13 & v14 will end up costing $600 total for a perpetual license user, assuming they stop raising their prices every year, it used to be $100 to upgrade now it looks like its $150.
The subscription model is $180/year, so thats $360 to get to the v14 release, $540 to get to the v15 release.
With the perpetual you can skip v13 and upgrade from v12 to v14 for a total of $450 (again assuming prices don't change), but if you skip both v13 & v14 you're back to paying full price at v15.
Of course the benefit of perpetual is you own the software, but if you buy a new camera you'll need to upgrade.