The ability to time your burst can be very valuable, depending on encounter design, as seen in midas and creator savage because there are a lot of short windows where you need to dps really hard to push/skip something. I haven't done enough speedkill attempts (group also not geared enough since we cleared a bit slow), but for example in o4s exdeath if you align your burst correctly (opener, after first tentacle, and after second tentacle) you can maximize dps to push the boss to 59.9% before he starts casting the second blackhole. That's how people could do 3:40-3:50 kill time on exdeath. For something like that, a job with bursty dps windows may actually be better than those with consistent dps. A very extreme example of this is faust z speedkill in a9s, the fight lasts 40-50s, so bringing 2 wars instead of any other tank compositions would be better, since 20s of that short window is spent in berserk. But that fight was so short that speedkill attempts are pretty much killing the boss over and over again until everyone in the group gets godly rng for their procs, in order to beat the top kill times.
As for what others said about being punished more if you lose time, yeah if you time it poorly you can lose uptime during your burst phase and lose a ton of dps, but on the other hand if you time it right you lose uptime during your non burst phase and be less affected than jobs with consistent dps.
