Yes she is.

[i]Yes she is.[/i]

... No seriously I've honestly never seen another version of Jack the Ripper that was more interesting. They usually go for "generic psychopath", which, um, I mean is quite possibly what Jack the Ripper was in real life, but that doesn't mean that in media you have to go with that interpretation. A sympathetic take(who is still kind of a scary murderer if you get down to it, especially if her Master is prone to that kind of stuff) is a lot more interesting. That and they actually explain the rationale behind her skimpy outfit. For once.

Anyway, as for the whole "balanced Grail War!" thing, that's an oxymoron.

The Grail War, in canon, was never, ever made to be balanced. It's repeatedly mentioned that some classes are inherently weaker and need to be sneaky and underhanded. It's mentioned a [i]lot[/i]. Yes, Saber is powerful(especially since Arturia is literally the best Saber [s]and best character[/s]) but it's not really rigging.

The Grail War is an inherently unbalanced affair, which is why you get some cheaty methods and underhanded, brutal tactics. Some classes literally need to do that to win. You're meant to play to your classes's strengths.

When it's Assassin, you go for Masters and try and strike when their Servant is distracted. When it's Caster, you play the long game and prepare as much as possible. Saber, you're up-front offense. And so on and so forth.

You really shouldn't be expecting balance.