Removing feature classes out of feature dataset would not help much to improve the performance. After all feature dataset is just a logical entity (unlike feature class which exists physically) intended for grouping of feature classes for various purposes. Following link has all the details:
ArcGIS Help (10.2, 10.2.1, and 10.2.2)
As far as locking and feature dataset is concerned,
" If you acquire a lock on a feature class within a feature dataset, the lock applies to the entire feature dataset and its contents."
Details about locking can be found on :
ArcGIS Help (10.2, 10.2.1, and 10.2.2)
Hope this would shed some more light on this....