OK, here's the easy thing to do, maybe post an image you think would be better with 1.2 or 1.4. Then we have something to talk about. It's unfortunate, but people like myself, listen to tall this ƒ1.2 nd ƒ 1.4 stuff. I bought my DA*55 50 1.4 based on the chatter. The way I shoot is I take 5 or 6 images at different ISOs and aperture settings and pick the one I think is best. I have not one image where I selected the 1.4. ƒ2 is the lowest that produces useable images. This year I have 3 ƒ2 images and over 2 BG of keepers on my hard drive. None of those three made onto Flickr for others to see, but they are still good enough to keep on my hard drive, in that there was nothing serious wrong with them.
SO seeing what you hope to accomplish would help. Maybe you can get what you want without going to even ƒ2.
"Also, a used K-1 will probably be easier to manage than buying new very wide F1.4 lenses for APS-C!"
ƒ/2 on a K-1 is the same as ƒ1.4 on APS-c. ƒ1.4 on a K-1 is the same as ƒ1.2 on APS-c. So, if you really want ƒ1.2 APS-c, if you go 1.4 on a K-1 is the way to go. Then you have tons of choice.
But I would seriously question wide angle and a ƒ1.2, especially on APS-c. Wide angle has so much more DOF. For isolating the subject from the background, probably the least want to use, is a 50 on FF. If you want extremely narrow DoF, FF is your best choice. Absolutely.
If you just want more light, a small sensor camera is your best choice. You get more DoF with the same amount of light with small sensor.
Small sensor, ƒ3.5, almost infinite depth of field. If this is your goal, use your iPhone 14. But, I really have no idea what your goal is. This FZ100 is almost the same resolution as my K-3 in LW/PH.
If you can more clearly define what you're after we can offer solutions. There are two aspects to a wide Aperture , DoF and lower shutter speed. Which are you after? They require different solutions.