That’s just now how it works. Muscle growth is caused by mechanical tension, which is the involuntary slowing down of the reps as you approach failure. Those reps where the velocity of the rep is slowed as the reps get harder, they cause the growth. Whether you’re doing 6 reps or 16 reps, you’ll still have roughly the same amount of reps that are experiencing mechanical tension, and thus, very similar muscle growth.
Also, getting stronger is caused BY muscle growth. The primary way to get stronger is by having larger and more powerful muscle fibers, aka, hypertrophy. I really don’t understand where this misconception that strength and hypertrophy were two different things, because they overlap a ton. The only big difference is that strength also has a neurological component, but outside of that, hypertrophy and strength are reliant on each other.
You have to at some point, it’s just how progressive overload works, which is required to grow muscle. The only ways to overload are weight and reps, and you can only go so high in reps before it becomes impractical. Don’t be scared to increase weight. Don’t increase too fast, use good form, and use weight you can handle and you’ll be fine.
The mechanism for muscle growth as we scientifically understand it simply doesn’t discriminate meaningfully across rep ranges. Proximity to failure to achieve high degrees of mechanical tension is all that really matters, so you whatever rep range you personally prefer will be great. If you’re indifferent, lower is better.
Strength and hypertrophy are very closely intertwined, as the only real factors in strength are technique, neurological adaptations, and muscle size. Getting bigger is the primary way to get stronger. A powerlifter specifically should absolutely be practicing 1 rep maxes because they will have to perform that in competition, but if you’re not worried about your 1 rep max, hypertrophy training and strength training are essentially the same.