A Krait moving at 500 m/s towards my t9 (not boosting) from 3 km away will close the distance at a rate of 400 m/s, arriving in 7.5 seconds.
A Krait moving at 500 m/s towards my t9 (boosting) from 3 km away will close the distance at a rate of 290 m/s, arriving in a little over 10 seconds.
When FSDs are cooling down, every second counts. Being able to completely disable my ability to boost with chip shots from a flak cannon seems like a pretty unfair advantage to my opponent. Like I said, this is all on paper, but what you're pointing to seems mainly centered around PvP, where equally matched ships are dueling, not the cat-and-mouse game of piracy/ganking, where getting away as fast as possible is the goal.
First of all why the Krait would be 3km away to start with (I'm assuming you are talking about the case after interdiction)? Even if so, why would you need to worry about drag in that case when you are already out of weapon range so you can't be dragged? Also when you are interdicted, it takes a while to deploy hardpoints but you can boost instantly and then fa-off to keep the momentum (yeah I know, that's not full boost speed).
Another thing is that it doesn't really matter if you are 3km away when any decent PvPer can do full damage with long range rails and lasers up to 6km. So a better question would be if you can flee to over 6km range if you have boost and I think we all know the answer to that. Frag pellets are also pretty slow so evading them from anything other than point blank range is quite easy.
You are very much correct about the time being important though so when I run trade ships, I boost past the opponent and high wake as soon as possible and hope the enemy doesn't have enough DPS to blow up my ship. This is actually where you can use turreted drag frag yourself to decrease the effective turning rate of your enemy when you boost past him so he has less time on target. Also compared to drag, screening has a lot more DPS so I'd easily choose that over drag to kill the fleeing ship as fast as possible. So for these kinds of situation the current drag is not the best choice for the attacker but it might give a little bit time for that fleeing trade ship if used correctly (because of the turn rate debuff, not the speed).
The reason why I talked about PvP earlier is that the whole denying turn rate by disabling boost is indeed very much PvP mechanics oriented where the pre April patch drag didn't do much anything because people could just boost turn to negate the drag debuff completely. Some vocal PvPers who can't handle that have just made it their mission to use ganking traders as an excuse to keep flying the way they have always flown, which is permaboost high turn rate and now they are worried they would have to learn to adapt. As many people have said already, heavily engineered PvP ships can take down trade ships with or without boost disabling drags.
