How much of battery drain is considered normal?

I have purchased a 15" MBP (MacBook Pro with Retina display, OS X Yosemite (10.10.5), Core i7 2.5GHz, 16GB DDR3) in Jan 2016. Though this particular model boasts of 9 hours of wireless web-surfing, I find its behavior pretty weird in recent times.

Just after purchasing this new piece which I could flaunt, I tried to gauge its battery performance since it is one of their prime selling point. As a test, I let YouTube video stream with audio turned on at full volume in Safari (since it's known to be optimized over Chrome/Firefox) for continuous one hour. To my utmost satisfaction, I found that 10%-11% of battery charge got dropped. Twice I tested, the outcome was the same invariably. Again yesterday, I repeated the same "experiment" once again. The battery charge got dropped 13%-14% in two runs.

Now-a-days, if I keep Safari open, do some amount of web-surfing, use Google docs/sheets, Facebook, video streaming (no Flash, gaming etc.), the battery drops around 20% in one hour. Point to be noted that I have installed a whole lot of software to exercise the full potential of the machine, but only handful of those, e.g. Dropbox, Little Snitch run as a background service consuming little CPU cycles.

As you can see, the battery drain has jumped from 10%-11% to 20% with a bit more of usage. That essentially translates to 5 hours of computing with a full-charged battery.

If I monitor the amperage, the full capacity of the battery (9 complete cycles so far) is around ~8600 mAh. Theoretically, to offer 9 hours of battery life, the amperage should be around -955 mAh while, with the usage profile mentioned above, it shoots up to -(1400-1500) mAh for no reason.

I apologize for writing a lengthy post. At the end, my question is if this drainage is normal? Earlier, I used a 13" MBP (no graphics card) for one month, the battery life was impressive (around 7-8 hours with full charge). That's what, I expected from my new MBP which is even twice costlier. I regret if I sound whining, but you very well understand how it feels one a device (supposedly) does not keep the promise and you have already spent your hard-earned bucks on.