Any improvements in the boosting process in the last few years?

[MultiBear]

Wow!!!

Is that speed improvement all from mage blinking, etc or is it also because the bonus objectives did not exist before?

The dungeon objectives make a massive difference, as does the fact that heirlooms can now be used all the way up to level 100. Before patch 6.1, their maximum level was 85, so for the 85-90 range you had to do without.