Do I need to say more? Grifts, even at fairly high levels are quite fast and fun to play - boss on the other hand usually takes FOREVER to kill.
Can you imagine how cool would that be not to have your good RNG rift ruined by lack of proper pylon at the end?
How cool would that be to kill boss in 3 instead of 8 minutes?
Of course good players would end up doing 55+ grifts again, even with the nerfed conduit - but who cares, it's just a meaningless number, everyone would end up a few levels higher in the end.
Edit: To elaborate, for those who are against the nerf:
Rift Guardian [Perendi, level 55] has 420,393,648,128 HP - I'm not kidding, this is the actual number.
Killing it legit will take EXACTLY 7 minutes, assuming 1 BILLION damage per second - which is absolutely impossible for most classes right now. You also have to dodge stuff, kite, run away, obviously. With taking that into consideration let's say 500,000,000 DPS is possible (well it's not really likely, but let's just assume that for a second) - there you go, 14 minutes to kill the boss alone, with already EXTREMELY high DPS.
The way game is designed right now requires cheesing conduit pylons to succeed, otherwise it is mathematically impossible to kill the bosses in 50+ rifts in time.
With the nerf of Conduits, it will now require conduit + power combo. I can guarantee you that top scores will be achieved like that, by those extremely lucky people who got both the pylons relatively close to each other.
If you think that basing the success on pylons is what makes the game "more hard", "more grindy" and "more skill based", well I really disagree.