That's very true.
And I agree, the game doesn't have to be made easier to play for players of all skill levels to enjoy it.
I think that's why Halo 3 was so tolerable. Once you got above 40, you rarely played with people who would be terrible or do dumb stuff. Proper matchmaking, especially ranked just works.
Though in regards to skill gap, reading the thread on what made Call of Duty successful, almost everyone agreed it was their low skill gap, carrot on a stick progression and hand holding and feeling that they are doing great.
Let's be honest, the majority of people at 343 play like BK's. You have them openly championing camo and boltshots in hallways.
Halo 5 needs to be a game that is easy to play, but hard to master. Despite what people say, it was pretty tough to 3sk people with pistols all the time in CE. Plus the fast movement and strafe meant that you had better defensive chances to avoid dying as well.