They are always slotted. :)
I've worked in machine shops and I've been in boatyards for 50 years and I've never seen anyone drill out a 1/4" S/S fastener in one minute - or two minutes or anything remotely close to that.
Not even on a drill press.
Even with replacement track you still have to get the old stuff off & out.
And then the fastener holes might not align so fill & fair and...
I would exhaust every other possibility before I resorted to drilling.
I have always been able to get track and the like off without drilling fasteners...
I forgot to mention - a cordless impact driver. I'm currently rebuilding my rig and I was very pleasantly surprised how effective it was.
S/S fasteners that had been screwed into the spar for 40 years came out with little trouble - well, all except one.
Soaked them with the heavy vinegar, hit...
Best luck I've had with S/S seized into Alu is high strength vinegar - "cleaning vinegar" or similar. I've seen it up to 20% - stronger is better.
It eventually soaks into the white oxide.
Also, a nut spun on enough to protect the end of the screw and then the big hammer.