Basement – Will fasteners straighten a pressure treated bottom plate

With steel sheetmetal studs fastened to sheetrock or plywood, the wall is plenty strong enough to securely support 200+ pounds—provided the load is attached and distributed properly. Either one alone (plywood or studs) can hold that weight, but in combination they are much stronger than the sum of their capacities.

Note that the floor will carry most of the load with the framing conducting the load downward depending mostly on the non-compressible aspect of the materials. If you are skeptical, visit a metal stud store, place one of the studs upright on the floor and stress it by pushing downward into the floor. The only way you can cause deformation is with a very large force (800+ pounds) or flexing it laterally.

I looked for specifications, but they are surprisingly difficult to apply to this use. If there is any doubt, you can always reduce the stud spacing to like 8 or 12 inches—They aren't so expensive that it would discourage a little overkill.

You could run your PT plates across the doorway to begin with, then cut them out after the fact. (Predrill the plate and use tapcon style screws and you won't split even a short bit of plate.) The upside of this is that you'll have a straight line across the doorway. Build a wall on this with another bottom plate/studs/top plate and it's easy to plumb it.

Alternately, you could skip the plate and attach the framing to the wall, but that could have issues with the lumber running nice and straight in line with your opening. Best practices would have you use pressure treated lumber in contact with concrete. (It's a bit of a waste of lumber to have 4 or 5-2x4s stacked up where you don't need them. Plus you'll have a hard time putting a light switch there.)