Tie rod end sheared off at the top

I take this to mean the ball and socket separated; is that right? If so, the stud that is still in the spindle is tapered. That needs to be a perfect, tight fit. It will hold the stud tight while you unscrew the nut. You do not even have to remove the cotter pin. It will shear off when you turn the nut.

Once the nut is off, use a hammer to pound the stud up, toward where the ball was. Tapping on the side of the spindle, right next to the stud, will also help break the taper. There was no need to grind anything off. Removing an outer tie rod end of this design only should take a couple of minutes. Where you can run into trouble is if that tapered fit is broken first, there is no easy way to hold the stud from spinning when you try to remove the nut. In that case we typically would use a torch to melt the nut off, but you can do the same thing with the grinder.

If the outer tie rod end was replaced or removed previously and the nut was not torqued to specs when it was reinstalled, it is possible for the stud to work loose. If that happens, the hole in the spindle will be worn oblong. The only acceptable repair for that is to replace the tie rod end and the spindle. If the spindle is not replaced, the new stud will not be fully supported along its entire length. It will be able to wobble and it cannot be held tightly in place. That will cause the stud to snap off or continually work loose.

If the tapered hole is okay, do not allow any dirt to get in there, and do not use any type of grease. The integrity of the mechanical connection depends on the friction fit between the two parts. It is acceptable to put a light coating of grease on the threads that connect the inner and outer tie rod ends together. That is the final "toe" adjustment during the alignment. A little grease helps insure that adjustment does not get rusted tight in the future.

Oh! Then I would use the angle grinder to cut the nut in half. If the taper is already broken loose, once the nut is off, the stud will just push out with no banging or frustration. If you have an air cut-off tool, that will work too but it will probably take a little longer.

The last alternative, and my least favorite choice, would be to weld a bar to the exposed end of the stud to hold it so you can unscrew the nut. I would only pursue that if the entire hole is covered and protected by the stud so no spatter gets on its sides.

You can also try using a large punch and hammer to force the stud tighter into the hole to hold it from spinning. I suspect that is going to lead to frustration because it is not likely you will get it tight enough that way.

My preference would be the angle grinder, and safety glasses!