I’m sorry but there is a woeful amount of ‘broscience’ BS in this thread.
Firstly, strength is a function of muscle cross sectional area and recruitment of these contractile fibres. There is no isolation of size or strength through rep ranges – if you disregard variables such as neural adaptation and exercise form in beginners, both strength and size will increase in line with each other or not at all.
The only way to consistently gain size and strength (there’s no either or) is to progressively load weight within a sensible rep range. Anything over 15 reps is generally considered to be endurance building and will have a lesser effect on hypertrophy – but the science pretty much stops there. Choice of rep range should be based on common sense and personal preference alone i.e. being able to maintain safe form, increasing weight without stalling. As long as you are progressively increasing workload and not letting it become easy, you will make gains. That’s all there is to it, anyone who tells you different is probably trying to sell you something.
As for muscle soreness, this is in no way an indicator of how hard you’ve worked. DOMS is thought to be caused (at least partly) by damage to muscle and connective tissue from lifting. The oldschool train of thought is that this is then how muscles grow (the fibres grow back thicker, stronger etc) – but in fact an entirely separate process called protein synthesis causes muscle growth. You stop getting DOMS after a few workouts as pain receptors become dulled, but protein synthesis still occurs up to a ‘cap’ rate. After this no matter how hard you destroy yourself, you won’t gain any more benefit, and you certainly don’t need to experience DOMS to reach this level.