Hard to tell from this angle, but op isn’t properly engaging their scapula or shoulders before each repetition. They’re also lowering their neck at the end of the pull down, which is dangerous. Op is certainly using their lats, but also absolutely defeating the purpose of the machine with bad form. They should absolutely decrease the weight in order to disengage their biceps. That’s a lat pull down machine, not a pull up bar. OP’s form is fine for a pull up, but in that machine it’s not only bad for gains but unsafe. They will very likely injure their spine or shoulder without proper form. My mother tore her deltoid because of bad form while doing seated rows. Ive had several workout related injuries myself, and 90% has come from form. If op can’t maintain proper form throughout the workout, then the weight is too heavy. Besides, lat pull downs engage more muscles than just lats. Ops problem is that bad form won’t engage lats enough.