A lot of other file managers just use the shell file copy routines, which aren't very flexible (e.g. you can't rename-and-copy at the same time) but are what some devices are optimised for in terms of exact buffer sizes and other nuances.
You can set up a button in Opus to copy things in the same way if it helps:
(I'd also be weary of comparing file speeds or times based on progress dialogs. For example, Explorer closes the dialog and appears done when the data is really only buffered and still being sent. Opus and Explorer measure speeds differently as well. The best way to compare is to open Task Manager's network graph and compare how long data is being sent for based on wall time. Caching and other issues also come into play, and if you are copying lots of small files then the Copy Attributes settings in Preferences can have a huge impact, but are less important if we're talking about a handful of huge files.)