If the original High Frame Rate (HFR) source was recorded with a (non DSLR) video camera there is a good chance that each frame has been created interlaced. This means that when a shot is not moving you have full resolution, but when you pan or the subject moves it will be separated across the frame in alternating lines.
If you remove half of those alternating lines by using "De-interlace" technique you only see half the resolution. If you blur the lines vertically a bit (like 2 pixels) you will get soft pictures that smear during movement.
The reason that the original looks good is because it is played back at full speed interlaced. But that is really 50fps! That is why it looks so smooth.
Its like a ladder has every second rung removed, making you jump each step. It looks weird. This applies to high frame rate footage that is recorded progressively (not mixed as alternating lines), where there are more whole frames. Progressive recording is better vertical resolution because movement doesn't smear across the frame in the same way.
One potential solution would be to try Optical Flow retiming. Some applications like FCPX or Premier Pro use this for slow motion but you can also use it to try and fix interlace to progressive. By adding a 0.5 or 1% speed change, the optical flow effect will try to make new better frames using all of the interlace information.
Alternatively you can get the NLE software to "interpret" the footage when imported so that the interlacing or alternate frame is merged 50% with the first frame in the sequence.
So in future, if you want to make a 24fps or 25fps project from HFR footage, I suggest shooting at a wider shutter angle to make the motion blur more pronounced or avoid fast pans.