Question about RPCS3 graphics scaling

In the blog post where the new high resolution feature was announced, it was explained that the base resolution should normally be set to 1280x720 and the desired high resolution output be set by the resolution scale parameter. However, I've noticed that when I use 1280x720 as base resolution while using the Vulkan backend, the text in the HUD and in-game looks rather fuzzy and pixelated regardless of the resolution scaling. Also, the 3D graphics look very aliased. However, when I set my base resolution to 1920x1080, the text looks sharp and 3D models much less aliased. It is as though the rendering is not actually being done at the desired resolution but rather the video output is being up-scaled. I'm using Soulcalibur II as reference for these tests.

If I used OpenGL, which significantly hurts performance in my PC, 720 base resolution causes aliased models but sharp text with 3x scaling or more, but 1080 base resolution fixes both.

Is this expected, or could it be my AMD R9 280 card not playing nice?

Summary
Condition: 720p Base 3X
Vulkan: Fuzzy HUD, aliased 3D models
OpenGL: OK HUD, aliased 3D models
Condition: 1080p Base 3X
Vulkan: OK HUD, OK 3D models
OpenGL: OK HUD, OK 3D models