That's a bit debatable. Nexo Knights was a relatively normal theme in terms of how it was marketed and the overall concept. It was given a show and a few mobile apps like Ninjago and the theme seemed to homage Castle and Space. Now I'm not saying TLG was just trying to tap into their current market, but they were definitely playing it safe.
Again, debatable. Nexo Knights was more or less the successor to Chima, meaning that it was intended to fill the void left from its absence. Additionally, unless NK's development was wildly different from most of LEGO's themes, the line was conceptualized late-2014/early-2015. Unless TLG wanted to doom their new BIONICLE reboot from the start, I highly doubt Nexo Knights was going to be a legitimate replacement.
Now I'm no philosopher, but I'm pretty sure an intellectual property created by dozens of people doesn't have the ability to deserve anything.
Technically two and a half, meaning it was able to last through three separate years and five major release waves. This isn't to say the line was a success because it probably didn't do too hot, but it was still able to hit the same mark set by Ninjago's original run and Chima.
G2 lasted two years, sure, but the circumstances surrounding that final year show that NK definitely did better for LEGO. BIONICLE only had four waves with the last one suffering through a limited release and as we established earlier, NK was able to get to the usual five.