Maybe the spikes you experienced were cause by this?
https://forum.defold.com/t/memory-leak-when-spawning-new-game-objects-def-1983/2716/4
Because of this bug i too almost implemented my own object pooling but luckily it was fixed in the latest version.
Maybe you can try to disable your pooling to test if the spikes you mentioned are still there?
My current project for instance creates several hundred objects each second on 3 year old devices without any spikes since the bug was fixed.