I have farmed neutral creep bosses and the drops dont help much, plus a lot of these neutral bosses are buffed as well, the increase in hero power is far lower than the increase in boss beefiness, percentage abilities are all that matter end game but your raw damage is just less relevant in anniversary, The bosses should not recieve such an extreme buff and enemy units should give more xp after they are buffed, not just bosses.
Anniversary has some interesting changes, actually.Goliath's destructive strike has a tiny, tiny cooldown
Infernal's ground smash is something like a 1 sec cooldown (which means more gold, xp, hp, str, infernal flame, etc)
Admiral's infinite growth is downright spammable as well
What I gleaned from the changelog is, that you are supposed to try to go for neutral bosses ASAP with your stronger abilities to gain strong items early.
If you don't take advantage of every little thing, then yes, this version is impossible past siege golem. but lots of strategies actually have more potential here