One slight advantage of the bolt on forks that I use under my bucket is : When cleaning sticks from my yard, after a storm or in the spring every year, the smaller sticks can go in the bucket, while the larger ones are out on the forks.
That saves me a trip back to the burning pile, compared to if I did that jobs with a bare set of quick attach forks. I suppose the clamp in forks would have that same advantage for that job.
For most other usage, the added visibility, by not having the bucket, would be a big advantage for the quick attach forks.
When I am moving mostly smaller sticks and light construction debris, I lay an old man door across my bolt-on bucket forks, and clamp that to the bucket edge with a single c-lamp thru the knob hole. That greatly increases the volume capacity of my bucket and is like having a dump truck available for lighter weight material.
That is a huge time saver compared to moving stuff with a trailer that must be manually loaded and manually unloaded.