Rag, Thrall, Greymane & Zeratul are all very good and popular picks in the meta right now. Butcher, Sonya, Artanis, Kerrigan, and Samuro continue to be among the top win rate heroes across all leagues.
The only melee heroes who see no pro play are Illidan, Alarak, and Valeera. All 3 are situationaly strong in the right hands in Hero League.
I guess what I'm saying is, I completely disagree with you. The melee assassin/bruiser role has never been so well balanced or fun to play as it is right now.
Rag is the most popular hero in the game and for good reason. He's sort of his own entity, though, as is Samuro who is really more of a specialist who controls the map than he is anything else. Butcher has an insane winrate which is a bit of a mystery to me. I only ever see them feeding, but picked in the right spot that is clearly working. Kerrigan is either gangbusters or just a busta and it depends on a whole lot of things from skill to comp to the enemy team's awareness/comp, etc.
Thrall (15.6%), Greymane (18.7%), and Zeratul (9.8%) are so popular that when you double their combined pick/ban rates they are
almost half as popular as Ragnaros (88.4%), aka, none of them are very popular. I would grant you Greymane and Zeratul certainly have their uses in drafts, but Thrall has fallen out of favor for some time now. His impact just seems far weaker, and I couldn't even tell you why to be honest.
The other two you mentioned, Sonya and Artanis are both bruisers and are part of why melee assassins are getting crowded out which is what the discussion was about.
If you look at the popularity for Hero League, Ragnaros is the only melee hero in the top 10 and he, Valeera, and Samuro are the only melee assassins in the top 25 pick/ban rate with Samuro sliding in at 24th. Considering 14 heroes are picked or banned in each game, to me that says a lot about how people feel about using second tanks and/or bruisers versus actual melee assassins for the job and echoes the sentiment put forth by Dunk/Bakery/Jake on the last THH about competitive viewpoints on them as well.
In those top 25 heroes, we have ETC, Artanis, Varian, Diablo, Dehaka, Muradin, Johanna, Anub'arak, Sonya. That's a whole lot of warriors and why not pick them over their melee counterparts? They are tankier, the often provide better or more reliable CC. Some specialize in destroying certain comps, others have huge sustain, and almost all of them do decent damage that can be buffed into pretty good or even great damage with talents. A few of the assassins have unique utility or matchups that make them OP for a scenario, but in general the philosophy in Hero League always seems to be to play the hero that fills the most holes in your comp while also generating the fewest drawbacks, which is kind of where Blizz has put the warrior role at this point in time. It's not so much the assassins are bad, just more that the warriors are plug-n-play and carry less risk.
