Reformer Pilates and a barbell program aren't competing for the same job. One builds maximal strength and size. The other builds the control, stability and range of motion that let you use that strength safely, and keep using it as you get older.
Most men who add reformer sessions to an existing lifting routine notice the same thing within a few weeks: heavier lifts feel more stable, nagging shoulder or lower-back tightness eases, and recovery between sessions improves. It's not about picking one over the other. It's about the strength training you already do finally having a foundation under it.