I won't say that Arrow completely rips off Batman, but the show borrows very very heavily from the Batman mythos.
Green Arrow has fought Ra's al Ghul; therefore, that aspect is not out of character either. The only plot point they took is the offer of leadership of the League of Assassins.
That's a pretty major plot point though, in my opinion. It's like introducing the Joker into the Arrowverse and having him be completely obsessed with Oliver. Sure, if you look hard enough into comics, you're bound to find a few where Ollie fights the Joker. But if they made the Joker obsessed with Ollie? It'd be a blatant ripoff of Batman.
I would argue the offer is more interesting here because Oliver might actually say yes; meanwhile, it was pretty obvious Batman would say no because he is so against killing.
This is a bit of a moot point though. Oliver, by virtue of being a good guy, was always going to say no. The dude stopped being an anti-hero and moved into kind-of-okay hero around 2 and a half seasons ago. I'd argue it's still more interesting with Batman, because, like you mentioned earlier, Ollie's motivation is redemption, Bruce's is justice. Ra's motivations fits better with Batmans. We don't gain anything new from having Ollie fight him.
And it is a blatant ripoff of a Batman plot.
Honestly, I think this is good because I think DC comics has handled Ra's poorly. He is supposed to be a global threat yet he only fights Batman. That never really made sense in the comics.
Honestly? True, I can see your point with this. But on the flipside, I don't see why Ra's would give a fuck about some random archer from Starling City either, y'know? If the show wanted to use Ra's Al Ghul well, they should, imo, have had him be a threat when the TV Justice League comes together. This is why I feel like at times the show is a blatant Batman ripoff. Ollie hasn't really done all that much to show he deserves the role of 'leader of the League of Shadows.' It just doesn't seem natural to me.
The show we have is true to character. It is just based on Mike Grell's Green Arrow. These stories were some of the main inspirations for the show. This Green Arrow was dark murderous and brooding.
Source? Not disagreeing, but this is the first I'm hearing of this.
Also, the bit where you say Ollie's going to become more liberal as he goes along? I sure hope so man, but from what I've seen so far, there's no reason to believe that's what the show is going to come to. I haven't seen anything to suggest that that's going to be Ollie's natural progression. Just watch the Flash/Arrow crossover episode. In the TV Justice League, Ollie's obviously going to fill in as their Batman. The episode had Flash drift too heavily towards Superman and Ollie too heavily towards Batman for me to believe that the show's going to turn Ollie around.