I think this:
However, those descriptors gave a bit too much flexibility/dynamism to the class shape in order to be efficiently optimizable.
means:
However, because those descriptors were gave so much too much flexibility/dynamism to the class shape, it could not be be efficiently optimized.
rather than:
In order to be efficiently optimizable, those descriptors gave much flexibility/dynamism to the class shape.
In other words that flexibility/dynamism hindered optimization; it wasn't for the purpose of optimization (as "in order to be" could be interpreted as).
The "too much" wording also contributed to the confusion for me.
But maybe just dropping "in order" would have been enough for me:
However, those descriptors gave a bit too much flexibility/dynamism to the class shape to be efficiently optimizable.
or
However, those descriptors gave a bit too much flexibility/dynamism to the class shape for them to be efficiently optimizable.