You can’t grow new muscle fiber, you can enlarge your existing fibers (hypertrophy) or improve your ability to use what you have (strength)…or both. You can only gain weight by increasing your caloric intake above your caloric expenses.
Or should I spend 4-6 weeks doing 3x8 and adding some mass and then lower the reps to the 1-5 range? Too most ppl this maybe isn’t too much of a concern. But my bench press is embarrassing. I haven’t made considerable progress in 4 years now…!!
That’s old style linear periodization. Whether you call it complex, concurrent or block training, working both qualities, mass and strength, at the same time is the better way to go.