Hard to tell in pic, is that a little hole at the bottom of the dent or just carbon?
If it’s a hole, no question it needs to be filled and smoothed.
Before I had a welder for this kind of thing I probably would have dressed the edges to flatten and round them and called it a day. There is crevice volume by the plug, head gasket and other areas. They just round it off to reduce hot spots. Depends on your tolerance for risk…
Bikes like this are very high hp/cc, any irregular bump like this, even sanded down, could cause a problem. I’d see what a machine shop would charge to fix it the right way.
While you’re at it, you might get a price on a complete top end job. They will probably remove the valves and associated hardware before machining the head anyway.
I think a replacement head is the best option. Welding that hole up will quite likely distort the exhaust valve seat which is next to it. That will in turn lead to a burned valve/seat.
The only way around that is to perform a complete valve job after the welding is done.
