The cannons from the 109 E don't do much dmg, the cannon from the F4 kinda does. F4 one of the better planes imo, but I thought the F4's and higher were good planes all the time anyway, so I don't understand what surprises you that much. Actually the F4 is one of my favourite planes right now
If you ask me, along with the climb, it maneuvers very smoothly and the cannon seems to be pretty accurate compared to other planes' cannons. And with proper use of flaps the turn is surprisingly good as well. So all these things together make it a very good plane.