(H) means 25 man in T8. Which means normal by todays standards.
Heroic raids did not exist then. It was activated hard modes.
There was not tracking for 10 mans as nobody cared about them, people were raiding 25 man and 25 man was considered "Heroic" and HC by current standards was the activated HMs.
If you raided then you would probably know that.
This is the problem. We have people that did not play 4 years ago that are arguing against people that did and pretending to know more than they do about it. People are saying "T15 is so much harder than T8" when they never even played T8.
That is why these discussions is impossible. You are trying to talk about stuff you know nothing about.
If you want to compare heroic kills.
1.5 months into T8, you had 0, yes 0, null, zero, kills of Alone in the Darkness (H), which was the final raid encounter of T8.
1.5 months into T15 we have 83 kills on ra-den. 83 > 0.