I think the Seafire counts as a 7th Spitfire variant, which makes it the aircraft with the most variants in AH. The 109 saw combat years before the Spitfire but has less variants in the game, so no complaining please.
Your forgetting one -
Fair enough if you include the Seafire, Tempest, Tiffy and the Hurricanes you have a total of 11 British frontline fighters. Remember we were limited in resources so didn't have the luxury of developing and building lots of different aircraft.
So yes you would expect the major plane in the RAF frontline fighters to be the Spitfire series.
For me the perfect RAF Spit line up is -
I
Vb
Vc
IX
VIII
XII
XIV - doubles quite effectively for a 1943 LF IX or mid 44 LF IXe
XVI - free
F.21 - perked
Seafire LIIc or III (not current one)
10 variants that cover from 1940 through till the very last engagement of WWII.
More importantly every major development (XII was first use of the Griffon), and most manufactured Spits. Would also give the RAF a true 1945 based aircraft, the F.21. which it is lacking at the moment.
These with the other ones would give a total of 14 British frontline fighters.
Try adding up the German and U.S. frontline fighters. I believe the U.S. ones already stand at possibly over 20.
Considering the 109 AND 190 were the Spits main adversaries, you can't seperate them, they should be added together also. Add to them the Me262, Me163 the LW isn't that bad off either.
So its not quite as easy as saying there's 10 and thats enough.