Congrats on the bike. I was decideing between the 7.3FX and Giant Rapid 3 last year. Ended up with the Giant because it was sportier, but it was a tough decision.

I, too, get hand fatigue and have to work on my positioning. Bar ends are a great recommendation. I have bar ends and they're a huge help, much more comfortable than the flat section IMO. I'm actually on the bar ends the vast majority of the time, and really on the flat bars only to brake... shifting is even easy from the bar ends.