From an App Rad point of view, the situation is not a loss of sep at the time you describe as you have not come below your minima of 1000' OR 5nm and they are diverging. It would only become an issue if there was a vertical sep of less than 1000' And less than 5 nm (3nm in our zone)at any time.It is difficult to judge without having been there but if you were training then your mentor is probably correct in making sure standard sep is achieved before you climb/descend/turn towards another a/c. It is a bit like don't do as I do, do as I say. When valid, you can make your own mistakes and take shortcuts as it then on your license