I find it very difficult to discuss rubato issues in an abstract way.
It should be stated as concrete as possible: in which piece, in which bar, on which note the tempo enlarges or speeds up. And why one thinks, you should do this - or why you should not, in this special case. Some people think, they are on the save side, when they play as the metronome ticks. It might be the save side, but it doesn't prove anything except that you can play very evenly. A machine can play very even too, but does a machine play better musically?