How about regrinding that face, as in your first picture, and then heat it up to red hot, and quench in oil to harden it. Then, just put it on a cookie sheet in your oven at 450 degrees for 2 hours to temper it, and let it cool down over night. I think you will get better sparks, and the frizzen will take the blows from your flint better. From what I see is being done to your frizzen now, you wore right through that thin case hardening with the first blows with your flint.
You should not have grooves running across the face of the frizzen. You should see strokes from the point of contact to the bottom of the frizzen face from SCRAPING metal off the face, and not gouging it. The horizontal grooves indicate the frizzen is gouging the frizzen face, which means it is still not hitting the frizzen at the correct downward pitch or angle, or the frizzen is too soft. I think the problem here is the frizzen is not properly hardened.
The bevel on that cut flint, or agate, is wrong, and not giving you the clearance you need. That should not be a problem now you are using the black flints from England.