H5 is laughably healthier competitively than Reach and 4. It easily rivals the Bungie games, and probably beats them in many regards.

Not when you consider the prize pools. Halo 2 and 3 generated a large amount of interest even with relatively small prizes. Of course Halo 5 is going to attract a certain level of competition when Microsoft is throwing such a large amount of money at it.

There was way more 360s sold when Halo 3 came out than xb1s when Halo 5 came out. Regardless, it was a more recognizable brand at the time, so it would obviously get more sales and have better population. Halo 3 sold 14.2 million copies by 2012. An obviously extremely impressive number. The Xbox 360 sold 76 million copies by 2013, (I can't find any numbers for 2012, so if there are any, let me know.) Let's assume that Halo 3 sold 1,000,000 copies from 2012 to 2013, that would bring the total to 15.5 mill/76 mill. Giving Halo 3 an attach rate of 20.6%. Halo 5 sold 5 million units in its first 3 months. In April, it was revealed by EA that There were just 18 milion Xbox One's sold. Assuming that Halo 5 had, let's say, a 50% downgrade in sales per month, then it had sold 7 million copies by April. Giving it an attach rate of 7mil/18mil, or 38%.

Yeah I'm not going to fact check all of this, I'll take your word for it. And yes, there were a lot more 360's out there when Halo 3 launched than Xbox One's when Halo 5 launched, however I truly believe the reason Halo 5's population is so low is based around its gameplay. I'm not saying it's bad, (even though it's not my cup of tea) but it is pretty far removed from the way Halo played in its prime.