Yes, that many Flamestrikes are excessive and actually not advised. What this does show though, is that Flamestrike in the basic/common slot for arena means it's fairly likely to appear at least once or twice (zero is rare but can happen) and has the potential to show up quite frequently.
|Is this "too good" as a basic in arena?|
It would be nice to simply make Flamestrike a rare, but that screws up the mage's basic card set. You'd have to shuffle things around and it would make a mess of players' collections.
Additionally, fixing one card to help balance arena can quickly bring on a number of other problems. You're going to have players crying foul towards other cards that are seemingly too strong when drafted more than twice, and a number of those complaints will be valid. A "slippery slope" scenario (say that five times fast) can arise where even more cards are changed or restrictions are placed on draft choices, which would take a lot of the unpredictability (and fun) out of arena.
As it stands, mage doesn't see all that much constructed play (though paladin is probably the least popular) so it's not the worst thing ever if they get to shine somewhere else. Just keep in mind that when you enter the arena against a mage and you're wondering how many Flamestrikes they have, it's probably correct to assume the answer is "Enough".