Sorry to circle back to this, but I needed my DMG for 5e encounter math, and I kept being either AFK or AFB...
a Deadly encounter for a 20th level party has an XP threshold of 12,700. 2x Storm giants and an XP threshold value of 40,000 for a group less than 3 PC's.
That's per PC, of course, but, yes, even a single Storm Giant is probably going to be a problem for a 5e Fighter 20.
So yes, within BA I would expect a 20th level fighter to lose to 10 Storm giants. But they might seriously be able to take out 10 Hill giants
Hill Giants are CR 5 (1,800 XP). 10 x 1800 = 18,000
Adjusting for numbers, that's 2.5, shifted to x3 for a "party of less than 3..."
54,000 vs that 12,700 deadly threshold of the 20th level fighter.
So 5e's encounter guidelines agree with Hussar that the greatest of fighters (or any other lone PC, in theory) can't just up and kill 10 giants, not even the least of true giants.
But, hey, two other eds have encounter guidelines... And, they're easier to remember, so:
3.x
Hill Giant is CR 7, making it a standard encounter for a party of 4 at 7th. Each 2x the number of monsters is +2 EL, so 8 would be 13th, and 16, 15th, so call it 14th.
Same applies in reverse so a party of 1 is very roughly equivalent to a party 4 levels lower, thus those 10 hill giants are theoretically a speedbump - for a fighter of 18th level (or any other 18th level character... according to the EL calculations, which don't adjust for Class Tier or anything).
4e
The least of true giants would be minion 13 Hill Giant Thugs. 5 minions equal a standard at paragon, so a 13th level fighter could take 5 of them as an ordinary encounter. Monster exp values double at 5 level intervals, so (coincidentally) an 18th level fighter (or other lone PC) could take all 10.
...
Of course, that's just what the guidelines say. A 13th, or even lower level 3.x chaingun tripper on Enlarge potions could probably mow through 10 hill giants. Likewise, in 4e, with Cleave, C&GI, and/or other close burst exploits - or, particularly, the notorious minion-blender stance, Rain of Steel, available as early as 9th.