Although at the lower right of the Vegas window is the time listed as you like, but it's in such an obscure location and on a 4K monitor, really tiny, that it is easy to over look.
So yes, I would like both a counter of frames AND time in the Preview window.
The benefit? if there is any issue during the render one can see exactly where it is, simple.
What kind of issues are you looking for during rendering? On default, preview shows only every 5th frame during rendering, so the chance to see a wrong frame is 1:5.
Maybe if it failed to render, give a time stamp of where in the video? I have another editor that does that so you know where to look to see where the problem is.
Part of the problem with using MMSSFF is that it is not an accurate timing. It is based on what you start your timecode on the timeline. Most people start it at 00:00:00, but not always. So then then counter has to reflect Timecode as opposed to time.
That's how I do it. Change the main timeline counter, double click on it, type the number, and it goes there. In Sound Forge, however, simply typing Ctrl-G pulls up a GoTo dialog box. I think that approach is better.
If you select the timecode window at the bottom right, you can choose what format it shows. Make this match the frame count. You don't need to change the timeline itself.