It seems like the EF 15-35 wins at the edges. But EF 14-35 is certainly "good enough". In addition to Gordon Liang's RF 16 f/2.8 video where he compares all there, there is this one showing the similar results between the RF 15-35 v RF 14-35.
But, looking at Neuro's and the images in this video, it isn't that the 14-35 is bad in the corners at 14-16 mm, just that the 15-35 is better.
Just be aware when looking at a comparison that the quality observed is relative to the quality of the other lens lens, and not necessarily an absolute perfect standard. Remember that the rating of the centre, mid, periphery and corners of a lens can be rated as excellent/outstanding, very good, good, fair and poor. We first need to know where the other lens sits on this scale to assess where its IQ sits on the scale. We can do this a bit more objectively than just say it looks fairly okay in the corners.
In Neuro's test, to my eyesight, the very the extreme corners of the RF 14-35 look soft compared to the EF 11-24 at 14mm f/4 and f/8 which looks quite clear. The difference can be seen in the edges of the bricks and mortar, which are more sharply and clearly defined, with better contrast in the EF lens images.
How clear is the EF 11-24 in absolute terms?
According to the extract from the Optical Limits review, at 14mm the center is 'outstanding' but the borders are just 'good' to 'very good', and the corners are only 'fair' at f/4, but when stopped down to f/5.6 the corners become sharp.
MTF (resolution) at 50 megapixels
The resolution characteristic varies substantially across the zoom range. Of course, the most difficult setting remains the 11mm setting. The center quality is absolutely stellar even at f/4. However, the borders/corners are soft here. The extreme corners show CAs with a width of up to 8 (!) pixels which has certainly also affected our tool here . Stopping down lifts the quality in the outer image region but not quite as much as you would have hoped. The best quality is reached at f/8 with good to very good borders and fair corners. At f/11 diffraction is already limiting the results.
The situation changes completely at 14mm and 18mm. The center remains outstanding but the borders/corners are MUCH better. The borders are good to very good at f/4 whereas the corners are fair here. However, the corners are boosted to sharp quality at f/5.6 already.
The performance goes a little downhill at 24mm again with softer results at f/4 and f/5.6 but f/8 is decent actually. The centering quality of the tested sample was good but not perfect.
Canon EF 11-24mm f/4 USM L - Review / Lens Test Report
www.opticallimits.com
If this evaluation is correct, then the comparison against the 11-24mm @ 14mm and f/4, which is only rated as 'fair' in the corners at these settings, shows that the 14-35mm can't match that, and in absolute terms, must be producing corners that would be rated less than 'fair'.
Whether that performance rates as 'good enough' for a particular individual's needs is a completely different matter.
Hope that provides some clarity in terms of absolute vs relative performance.