I don't get this problem, maybe your computer is really slow? Here's two things to try.
Open up ...RebornBuddy/Settings/YourCharName/MagitekSettings.json and replace the number in line 20:
"PulsesPerSecond": ##,
with a lower number and see if that helps (I'm not sure this is actually implemented anymore).
If not, try opening task manager (Ctrl+Shift+Esc), right click RebornBuddy.exe > Set Priority > Below Normal.
Let me know if that makes it any better. I swear there used to be a text box in excombatassist or magitek somewhere to change the pulse rate, but it looks like it's not there anymore or I'm just missing it.
Yes I find it weird as well. My PC is quite new, and able to perform maximum and ultra on the most recent stuffs. I seldom use SCH, but when I did on the older versions of RB previously, this problem didn't occur as I did also do DPS as a SCH. Also experiencing this "lag" after lowering all the graphic options to low.
What exactly does the Pulses Per Sec settings do...? By default it was at 30, I changed it to 5 and noticed only a very very small difference. Doesn't happen on other jobs.
How do I set Magitek to spam skills less often in terms of for example:
[02:41:02.207 N] [Magitek] Casting Bio
[02:41:02.207 D] DoAction Spell 164 0x40031AF4
[02:41:02.230 N] [Magitek] Casting Ruin
[02:41:02.230 D] DoAction Spell 163 0x40031AF4
[02:41:02.263 N] [Magitek] Casting Ruin
[02:41:02.263 D] DoAction Spell 163 0x40031AF4
[02:41:02.283 N] [Magitek] Casting Ruin
[02:41:02.283 D] DoAction Spell 163 0x40031AF4
[02:41:04.816 N] [Magitek] Casting Ruin
[02:41:04.816 D] DoAction Spell 163 0x40031AF4
[02:41:07.266 N] [Magitek] Casting Ruin
[02:41:07.266 D] DoAction Spell 163 0x40031AF4
[02:41:07.286 N] [Magitek] Casting Ruin
[02:41:07.286 D] DoAction Spell 163 0x40031AF4
[02:41:07.315 N] [Magitek] Casting Ruin
[02:41:07.315 D] DoAction Spell 163 0x40031AF4
[02:41:07.337 N] [Magitek] Casting Ruin
[02:41:07.337 D] DoAction Spell 163 0x40031AF4
[02:41:07.366 N] [Magitek] Casting Ruin
[02:41:07.366 D] DoAction Spell 163 0x40031AF4
[02:41:09.907 N] [Magitek] Casting Ruin
[02:41:09.907 D] DoAction Spell 163 0x40031AF4
[02:41:09.981 N] [Magitek] Casting Ruin
[02:41:09.981 D] DoAction Spell 163 0x40031AF4
[02:41:10.053 N] [Magitek] Casting Ruin
[02:41:10.053 D] DoAction Spell 163 0x40031AF4
Not try to cast something e.g. Ruin so many times within that 1 second Global Cooldown, just got a gut feeling maybe this is the cause.