Reaper main? Fractal farm?
I have yet to find anyone that has complained about what class and/or build I play as long as I perform the mechanics properly. If you want to learn more about builds for raiding and fractals, I would suggest: qtfy or metabattle.
As for your question to revs, all classes are viable anywhere, it’s just that most people get caught up with what is optimal, in the theory that it would allow them to finish the content faster than a non optimal group.
I don’t know where you heard that Viper Reaper is not good in fractals as it is the king of fractals. Even with the recent changes to Epidemic, when you have more than one reaper, groups of enemies melt fast. In fact you often see groups of 4 reapers and a druid/ele (I have been part of such groups myself) and they tend to melt enemies in seconds.
Depends on what kind of runs you’re looking for. If you want things to melt, as stated above, a party of 4 necros surely isn’t optimal. If you want to get into better groups where you actually melt stuff, with a chrono, druid and ps warrior, you’ll have a harder time finding one than eles/thieves/crangers/engis/guardians do. But with that being said, if you like reaper, go for it. It’s not as bad as most people think it is, quite high dps (~32k if i remember correctly).