Or rather, it looked like Kensuke had arrived at the studio at the same time as me — the other two were still running late.
Literal
Or-rather Kensuke [subj-が] simultaneously studio [to-へ] arrived [seems-みたいで], other 2-people [topic-は] still are-late [seems-様だった].
ってか is the clipped/spoken contraction of というか — Japanese has many variations of this 'or rather / I mean' discourse marker (というか, っていうか, ってゆーか, ってか, つーか) all in active circulation. みたいで and 様だった are both inferential/observational ('seemed'), and their stacking gives a hesitant, secondhand feel to the description. 遅れてる is the casual い-dropped contraction of 遅れている.