I don’t think pace is a must in a great number 6, Fabinho was hardly rapid, but it depends on team around that player. With peak Van Dijk, Robertson and Matip/Gomez, it wasn’t a problem for Fabinho, but our current team isn’t as athletic overall.
Konate is an exception among our starters, but he alone isn’t enough and the 6 in the current team needs to provide fast running in addition to positioning and aggression. Not seen much yet of course, but based on the first impressions of Endo, he does not seem to be that sort of player unfortunately.