Not everyone can play every role. I love Patrick Stewart, for example, but even in his prime you wouldn't hire him to play someone like Iron Man (even ignoring the different nationalities). That said, shitty actors win awards all the time, see Jared Leto and Joaquin Phoenix who are both academy award winners even though they both suck (for different reasons, admittedly). Awards just mean film snobs like them, and there is a certain style that is almost guaranteed to get awards from film snobs regardless of actual quality. So, this woman getting awards for a shitty TV show that critics like means absolutely nothing.
The general audience doesn't give a shit about Orphan Black, period. I'm a huge nerd who basically doesn't care about anything that isn't Sci Fi or fantasy and I've barely heard of the show, people who aren't interested almost exclusively in genre content like me probably haven't even heard of it. She probably has the name recognition of the C-list TV star at best among a general audience.
As for the show itself, its badly written crap that only lasted as well as it did because some people fell in love with its central gimmick, which was only that: a gimmick, and not a well done one. For example, Brent Spiner did a much better job playing 2 identical looking characters a few decades ago then this woman did playing multiple people. That's why Orphan Black is a fairly obscure show, and only lasted as long as it did because it was a Candian production that was shown in the US on a network that doesn't get that many views anyway. Glancing at some TV ratings online, if it had aired/been made by a more mainstream US channel, say SyFy or USA Network, it probably would have been cancelled quickly.
Jennifer was definitely younger then Bruce, in the comics having a 5 year age difference (according to a quick google), but Bruce Banner isn't supposed to be in his late fourties/early 50s like Ruffalo is. Ruffalo works for a movie franchise where Bruce has been active for years before The Avengers and Ruffalo only has to show up a handful of times before eventually moving on, but generally you want to start younger, and She-Hulk was definitely not past her mid twenties in her first appearance, and with comic time she's probably barely 30 if that in the comics.
But, again, with a better actor the age would be less of an issue. Ruffalo happens to be 1000x the actor that Norton was, and RDJ is an amazing actor (especially in the role of Tony Stark), so them being too old isn't really an issue (and honestly Stark's age can work older or younger just based on his origin).
Its nothing to do with her as a person, C-list TV actors are going to be cheaper then movie stars or even A-list TV actors. To use different actors as examples, Patrick Stewart is going to cost more to hire for a show or film then Scott Backula. That doesn't mean that Backula is a horrible actor (although he isn't anywere near as good an actor), it has to do with experience, name recognition and popularity.
