I agree, that the arcanocrystal was mainly a problem with making a too powerful item, but it also showed that in a world with TF, Blizz can no longer really make super powerful items designed for a single tier, since the rest of the expansion might be affected its pressence. It is not a big minus in the book for the overall gameplay experience, but it leaves a big trap hole in the design process, where any good item might create the arcanocrystal problem again.
When it comes to the TF system in BFA, i will say this:
- Yes, the changes to the system in BFA will nearly without a doubt create a more rewarding experience for going into harder content. I don't know how much it will be better, but since we don't have legendaries anymore and since azerite gear are not affected by TF, we will without a doubt see a more people enter into a harder content tier with gear, that can be upgraded by the boss drop from those tiers.
- For this, i am not quite sure. Even with the removal of legendaries and the smaller pool of upgradable items, TF is still gonna have some form of effect. Watcher said at Blizzcon, that they are looking at tweaking the chance for TF to be even lower and maybe they can make it so low, that you can't really count on it happening over a reasonable X amount of boss kills. If that is the case, i would say that the continuous upgrade structure can be returned to a healthy level. If that is not the case, i fear that we will still see people, especially going from heroic to mythic, find that the reward for going up in difficulty is simply too small and that repeating the already beaten content is suffecient enough, even with not getting upgrades for azerite gear.
But yeah, overall i think you are right. We should really be looking towards the new system in BFA more. There are still many factors still unkown about the system in BFA, the game is still in Alpha so much can change, but there are still things like Azerite armor, weapons and the removal of legendaries to talk about