This is a good question. I think several ergonomic factors would make extended reverse operation more difficult, e. g.,
the wind into the open cab, the throttle and brake arrangement, forward visibility, probably others. And they likely
would not push a train very fur or very fast on a main line (altho I think I've read that they do now on some lines.)
I don't know, but assume, that valve timing would also affect the performance and efficiency of reverse operation,
unless it was compensated in some manner. It would be interesting to read more about this.