Well I was just offering advice not trying to argue whether or not Armor Lock is cheaper than Sprint. But since you're offering...
As far as slowing down matches and all that stuff, the only problem I have with armor lock in that sense is that it robs people of assists. They're janky and hard enough to get in Reach without the armor lock.
The way I know Armor Lock is unbalanced is because I play Arena with Hologram exclusively and if I used Armor Lock, I know I would have much fewer deaths. If I see a grenade coming, it won't hurt me. If I get stuck, I'll survive. If I'm one shot, I can at least live for a few seconds longer. It's also good for baiting. People seem to just watch people armor locking waiting for them to come out. I do this too. Lol, I'm still trying to figure out what to do.
I just go by how I feel. I feel cheap using armor lock. With Hologram, I feel like I'm at a disadvantage and it makes the games for challenging and fun for me. You wanna bring Hologram up to the level of the other armor abilities? Let me stand on my holograms head. Oh man that would be amazing! I think that would make it over powered though :lol