<What should I merge?>
Erik didn't absorb new brain crystal powers until now. Shade's one was the only exception he made, and the reason was that even having all those, even with his insanely strong training technique, was taxing, and things were becoming much harder as the number of neural links increased.
Not having the time to train all those powers made it superfluous to add new ones. Aside from that, merging powers had a huge downside: losing the neural links.
Erik had thought many times about getting a lot of them and training them only at the initial levels. That would have increased his strength by a lot, but the powers' efficiency would have remained low.