I'm not sure how much Year 2 you've actually played. Doctrine of Passing is an autorifle and was legit top-tier, able to unseat TLW even. Hand Cannons have made a major comeback since April, with Eyasluna and Finnela's Peril being popular and strong choices. Even Universal Remote is a top-tier choice, which anyone in Year 1 would laugh their ass off at.
Trials of Osiris' Top Guns for July
1) Hand Cannon
2) Scout Rifle
3) Pulse Rifle
4) Auto Rifle
5) Universal Remote
That's literally every weapon class. You know what's not on that list? PDX & Hawksaw. MIDA is #2, but guess what, the last week of July it dropped to #5.
So many guns are viable now. And 6s has even more guns that pop-up, like Answering Chord, Colovalence's Duty, Bad Juju, No Land Beyond, etc.
Year 2 is definitely slower than Year 1, and I get a lot of people don't like that. But year 2 being less diverse than Year 1 is plainly untrue.
(also, your statement that all guns should be viable at all distances is not how the Destiny sandbox has ever worked.)
I ... I don't see how Trials of Osiris as a way to show what weapon class is being used the most. I've played my fair share of ToO. People always pick what is currently THE best weapon available and tend to focus their choice on the map. You are correct that these weapon classes ARE being used though. However, it's the MIDA, PDX/Hawksaw or Doctrine. I barely see anything else. And I know, because when I die I take a look at what weapon the enemy is using but nothing ever suprises me. Sure, there's sometimes a handcannon user, or someone with a different weapon but most of the time they switch back to something more deadly.
And Doctrine overclassing Y2 TLW is pretty easy. A good TLW user can be dangerous but the gun is nowhere where it used to be. All in all, its a matter of personal opinion isn't it?
In the end, it's just a matter of opinion. I find Y2 to be lacking in terms of weapon choice. Something Y1 did better. I see Y1 as being much more fun than Y2. Y1 contained more weapons that were actually pretty good. Y2 has a much smaller pool of weapons that are effective. You can still use a weapon from each of the weapon classes but the choice you have is much-much smaller than it was in Y1 IMO.