I said it before and I'll say it again, incremental improvement system for playing the game is a GOOD thing to me. Knowing that just by playing, without any luck involved, I can work towards small improvements in my character is very nice. Not my fault that some people have no self control and have to "finish" the system by grinding content over and over as opposed to just having it happen naturally by playing, or that there are crazy guilds that require that kind of effort to be put in. I haven't done a single piece of extra content designed to grind AP, and I'm at 13/20. If I was a DPS, that means there would be a 3.5% DPS difference between me and someone who grinded Maw until his nipples fell off. Would it be more tolerable to people if each point was a 0.25% DPS increase or something? Or would people still feel the need to grind 1000 Maw runs for 5% more DPS? At some point, you shouldn't take progression away from players just because some people cannot exercise self control.
Now, there are certainly problems with the AP system, but it is certainly more good than bad. Main problems include the fact that dungeon AP is not tied to dungeon length, but this is being fixed in 7.2. Another issue is that raids don't drop enough AP, each boss should be guaranteed to drop an AP token at the minimum, certainly each raid boss on Mythic should drop AP equivalent to a Maw run at +10. Some people think that there should be a limit on M+ AP, but that is stupid. The point of AP is that all content you do rewards you with something. If you limited M+ to only give X AP per week or something, crazy people would just switch to doing random heroics non stop for AP grinding, which would be much more boring and people would complain even more.
I don't like that it "locks" you into a spec, but I think the effect AP has on this is overstated. You can VERY easily get an offspec to finish their weapon at AK25 and pick up the 5% DPS paragon. At that point, you are only 10% behind someone who has fully finished their weapon. And honestly, your alt spec should be 10% behind someone's main spec, that seems fair. But you can also be easily fully functional at that point, and you can finish an off-spec weapon to the 5% paragon in a week of WQs without any M+ runs if you want, so it isn't that prohibitive. I think spec specific legendaries are MUCH worse for switching specs and playing off-specs than AP is, and this is coming from a Druid, the one class with 4 total specs and artifacts to level up.