You've mentioned both strength and LBM development, and these aren't all that related as you might think.
An untrained individual will have greater muscle growth simply due to the fact that they are untrained. As in, their body has never been introduced to this external stress and stimulus caused by weight training and as a result, it adapts to these new conditions, and grows. This rate is of course higher for untrained lifters as opposed to trained ones. You can convince yourself of this by just thinking, don't even need any scientific studies, although I'll link one at the end. Just think, if the rate of LBM development WASN'T higher in less trained individuals than trained ones, then wouldn't it become easier for bigger people to get even bigger than they are? What I mean is this:
Suppose that the rate of LBM development was the same or higher in trained individuals than untrained. Then, it follows that as you keep training and stepping more in the "trained" category, your LBM development would increase proportionally and you would keep gaining muscle indefinitely! I'm sure you now realize how absurd this would be... The world would be full of The Hulk. Look at professional bodybuilders or any strength/physique athlete, look at their development throughout the years...once they reach a certain size, they almost can never increase size.
Or just reach your own conclusion through big data! Look around in the world, how many people do you see that are lightly muscular, medium, and heavily?
This article can maybe shed some light on your concerns, and also look up the protein myostatin to understand why the things I mentioned above seem to be so.
Strength, however, is a different ball game.
Yes, strength will somewhat be related to the cross-sectional area of your muscle fibres (basically, somewhat of your muscle size), but it is primarily CNS driven. This may be where your confusion is coming from. Strength gains are mostly CNS while muscle gains are mostly due to adaptation and new stimulus. I don't want to write you an essay but this is the main idea. Your body, invokes different systems based on the different stresses that it is put under. If you do 6-12 reps with moderate weights, your muscular systems with type 2 fibres will step in and do most of the work effectively working hypertrophy. If you do 1-3 reps with very heavy weights, your muscles won't even have the time to be simulated enough and your CNS will take over with very heavy weights. What I mean by CNS is, basically, when you lift heavy weights, your body says "wow that is some heavy weight, I must recruit more of my resources". Well, you recruit more "resources" by recruiting more motor units (part of your CNS). More motor units = more muscles and tendons recruited = a stronger you. In untrained individuals, your motor pathways are very "dusty" and inefficient, since they haven't had to do this job before. It's basically their first day on the job in a way. But once you start training (first few weeks/months), your motor pathways start becoming more efficient and your motor units become better at their jobs (like any human working at any job, they will get better over time, they will adapt), your motor units adapt, and as a result you get stronger.
So, just think in terms of strength (CNS) and muscle growth (hormones, stimulus, anabolic environment due to diet and etc.) They both use different muscular systems which is influenced by your rep and weight ranges, although there is some overlap obviously (2-6rep range is decent overlap).