IMO, yes a 5 shot revolver has enough shots to enable you to fight back in MOST situations and it'll give you a pretty good measure of protection. Will it always be enough for every defensive situation? Probably not. But in most situations where pulling a gun out on somebody is necessary, most criminals usually decide that it isn't worth their trouble to keep bothering you and they usually take off before you have to shoot them. In the vast majority of cases where people use a gun to defend themselves, merely showing it is enough.
Say that they don't take off though and say that there's three or four criminals attacking you instead of just one. Would five shots be enough then? Maybe or maybe not. Just shooting one or two of them might send the rest into flight and you may not have to shoot the rest of them/shoot at them. Say these three or four guys have guns themselves though, what does that do to your chances?
If you had a compact semi-auto like a Kahr 9mm or .40 S&W, you'd have basically the same number of shots (actually it's +2 rds for the Kahr, 1 in the mag and 1 in the chamber, but it isn't a big difference), but you'd be able to reload much quicker. I don't think that the semi-auto is any more accurate or shoots any quicker than the revolver does mechanically, but it does have two advantages in actual performance.
1) It's much quicker to reload and it's definately much quicker and easier to reload under stress. When your adrenalines going, your heart is racing and your hands are shaking, which would you rather do? Try and fit a mag in the butt of a semi-auto pistol and hit the slide stop? Or try and fit five different bullets into five different chambers at the same time, twist the speedloader, tilt the revolver forward and then snap the cylinder closed?
Your fine motor skills degrade under stress, so something you do twenty times every shooting trip may not be as easy if your getting shot at or if you just shot somebody and you have to reload immediately.
2) A semi-auto pistol usually also holds at least a couple more rounds in the mag when fully loaded, even the compact models usually hold more than the revolver does. This gives you an advantage, especially when you're facing multiple opponents. It allows you to stay in the fight longer before reloading.
Most of the time though, you're not going to be getting attacked by one guy, much less by three or four. If you do have any problems at all, it's likely to just be one guy by himself. For situations like this, the revolver is perfect. Even in the situations where you're facing multiple opponents, it still might be enough if you shoot the armed opponents that represent the biggest threat and then you could retreat in a big hurry (which is what you should be doing anyway).
If I was going to carry a revolver as my regular carry gun, I might think about also buying a small .32 ACP or .380 ACP pistol as backup, just so if it was really needed then I could put out more rounds than what was in my revolver. Plus you may need a back up pistol, for whatever reason you may not be able to use your revolver (maybe your right hand is wounded and you can't get it out of your right pants pocket, or maybe you got blindsided earlier and they took it out of your hand).
However, if I was going to just carry a revolver all by itself, I'd pratice reloading ALOT with speedloaders. Two hand reloads, one handed reloads, weak handed draws, reloading weak handed with single rounds and with speed loaders etc. Because you may really need that skill one day.
Know in advance that you probably won't need it as far as the statistics go, you're more likely to get into a automobile accident than you are to get into a shootout with multiple assailants. But I'd rather have the skill to reload and draw the revolver weak handed and maybe have the smaller extra pistol as back up than need them both and not have either.
That's just my two cents though. In most scenarios the revolver by itself does fine.
