It is not as important. BUT there are benefits to emphasizing all three types of contractions.
The first one is simply the novelty of stimulus. Emphasizing the eccentric or isometric presents a different stress on the muscles which can help someone get “unstuck” when it comes to gaining size.
This is mostly true if someone has been training the same way for a long time. The body becomes really adapted to the motor task and as such there is no real need to further adapt. This is even more true when someone has reached a point where it’s hard to gradually add more weight to the bar. If you are adapted to the type of motor task and stress you are putting on your body and can no longer easily add weight to the bar, you can only change the type of stress or increase its magnitude (volume or frequency) if you want to progress.
Each type of contraction also has side benefits that might not be directly related to hypertrophy, but can help. For example eccentric actions will strengthen tendons and the part of the muscle closer to the tendons more than concentric actions. This can help reduce the risk of injury. It’s easier to train hard and grow if you are not injured.
Isometrics increase synergistic activation and stability. This also make you less likely to get injured while training. But by improving active stability you also improve performance. If you improve performance you can lift more weight which helps trigger more growth.
There are just a few examples. While you don’t have to put the same emphasis on the 3 types of contractions as an athlete, training them to some extent will certainly be benefitical.
I do use a different model for “pure hypertrophy work”. I’m coming out with new programs soon that illustrate that difference.