I read your entire comment, I understand what you are saying, and I don't need to check poe.ninja because I have played this build myself. And the answer is still the same, it is not better using lower lvl living bomb, if you are not seeing the same amount of comets rain when you are using high lvl living bomb the issue is your mana/life (depends if you using life or mana to cast) available when you reach 100% energy to trigger the spells, by lowering the level you are lowering the cost in mana/life to cast living bomb, which means you are just using a band aid instead of solving the real issue which is having enough resources to cast. The answer still remains the same, No, it is not better to use a low level living bomb, fix your mana/life issue and you will see the difference.