It’s a very interesting observation overall that both high contrast and low contrast can be good for accessibility.
We could consider our current symbolic icons a part of a “low contrast” mode, and give them some subtle color for a new “default contrast” mode. This could could be done via internal CSS, so it just turns on and off, no need to swap out a different icon theme. A high contrast mode would probably involve a whole different icon theme and dispense with the symbolic icons entirely in favor of full-color ones — which would of course need to be created and maintained, and that adds some risk. In the meantime, the new default contrast icons with a little but of color would have to suffice.
Considering how many people might have some similar needs as you have (might be as high as 1% IMO as already 0.7% are registered in Germany to have ME/CFS), it might even make sense for KDE to provide a “Low Contrast Colour Scheme for People With Neurological Conditions”. Of course for this we 1. need the idea, 2. a plan what to do, 3. agreement to the plan, 4. someone to work on this. Not sure though if there is some one-size-fits-many solution there in the first place.
Anyways, I am mostly rambling, but there is theoretically a way forward here.
The widget in 6.2 is known to be a little weird especially on different aspect ratios. I rewrote a lot of it in 6.3, and hopefully it’ll work much better.