Quite a few karate and wing chun students say that their teacher does a bit of taijiquan as part of the syllabus...
An alexander technique teacher in Bradford once admitted that she taught taijiquan as a cool-down despite having no knowledge of taijiquan whatsoever. Shame on you, Heather.
There is more to taijiquan than moving slowly.
Fundamental principles: whole-body movement, reeling silk, never tensing your muscles, circularity, not pushing, not striking-through, softness, yielding and looseness.
Do any of these factors apply to karate?