There's no such thing as a non-responder to resistance training,1,* you're just not eating enough to gain muscle.
* With the possible exception of people who have some certain types of muscular dystrophy.
There is also no reason to think that an individual would experience vastly differently responses to compound vs isolation exercises. Hypertrophy training will increase muscle mass in pretty much everyone provided that the right conditions for muscle growth are present, which includes adequate training stimulus, sufficient energy availability for muscle growth (either eating in a caloric excess or having a lot of body fat to start with), and sufficient sleep.
Here's a simplified table I just put together that will tell you the expected outcome for every combination of whether or not you have a sufficient training stimulus (volume and intensity of training) for muscle growth, whether you're eating enough, and whether you've already gained as much muscle as your genetics permit.
+--------------------+------------------+------------------------------------+--------------------------+
| Training stimulus? | Caloric surplus? | Already reached genetic potential? | Outcome |
+--------------------+------------------+------------------------------------+--------------------------+
| Inadequate | No | No | Lose muscle |
| Adequate | No | No | No change |
| Inadequate | Yes | No | Gain fat |
| Adequate | Yes | No | Gain muscle |
| Inadequate | No | Yes | Lose muscle |
| Adequate | No | Yes | No change |
| Inadequate | Yes | Yes | Lose muscle and gain fat |
| Adequate | Yes | Yes | Gain fat |
+--------------------+------------------+------------------------------------+--------------------------+
Now, notice that there are only two "no change" outcomes. If that's what you're experiencing, then we can narrow down the cause to one of the following cases:
- You're reached your genetic potential, and aren't eating in a surplus, but are training hard enough to avoid losing muscle.
- You're training hard enough to gain muscle, but aren't eating enough.
Given that you mentioned your body fat level being only 11-13%, it's pretty much certainly the second case. You need to keep increasing how much you're eating until you start gaining weight. If that weight comes on as body fat (assessable by measuring your waist circumference) then you would need to reassess whether your training program is actually adequate. But unless you've actually gotten fat while on a decent resistance training program, you really can't say that you're reached your genetic potential. This really needs to be emphasised - if you've stopped gaining muscle but haven't started getting fat then you aren't at your genetic potential, you just aren't eating enough.
Consider getting a strength training or bodybuilding coach to help you through the process. That will likely be the biggest single change you could make towards further progress.