Leeds fan here:
He wasn't slow at Leeds at all, his mobility was one of his strengths. He was routinely able to come into the right positions during 2018-21, but I've generally thought that was more about Bielsa's system than Kalvin.
Though this was also after some injury issues, I was distinctly unimpressed by his performances under Jesse Marsch.
Another poster above was right that his long passing is his only elite attribute. I did think his mobility and pressing was there too for us but it's not now.