Majoru Oakheart
Adventurer
As a note... 'just eating the fighter' is not really a valid response. A fighter backed up by any leader can probably hold off most solos until the party kills it, especially one that is unable to use special tricks, is forced to go after the person who has special bonuses on them (defensive stance, shield of faith, battlerager, what have you).
You can give the fighter bonuses, sure. But the math is pretty decent in 4e. It is rarely possible to make a fighter so defensive that you can't take him down if you are a monster with a level equal to or higher than the party. Especially a solo.
It will be pretty hard to take down a properly defensive fighter, I agree. A level 6 fighter with a constant +2 power bonus from somewhere and being on the defensive every round, a fighter who had +2 layered plate on and a Heavy Shield might be able to make it so a level 7 solo Red Dragon needs 13+ to hit him. It is still a decent chance of hitting and it does good damage.
Battleragers might have been able to do it before, but since the errata, they'll be in pretty much the same situation as everyone else.