Most people will tell you to stick to the A7r because its a more expensive, higher tier camera. But honestly, if you don't enjoy it, if you haven't taken to it, and if you already have K-mount glass, then getting a Pentax Kmount DSLR makes sense. I recommend you go to a store and try holding the K-3, K-1 and K-70. In your hands, that will be the tipping point where your choice will be made easy.
The K-70 does have good sensor and apparently has pretty good noise characteristics. Though, for landscapes, I generally use lowest possible ISO so noise is rarely a problem, even with my 16MP camera.
Better to have a camera that you enjoy, that compels you to go out and take good photos; than to have a camera with high end features that you practically never use. That's why I enjoy my silly yellow K-01 and don't mind that there are better cameras out there
So go ahead and go down the path that pulls you. Do a test run first if you can, but don't seek approval of your choices from strangers on the internet