Do clothes dryers have heat insulation that could be mistaken as lint?
No.  No such insulation that looks like lint.  Anything that looks like lint is lint and has to go.  Can use compressed air carefully to get at the hard to reach stuff.  However the more likely culprit is a blocked or kinked vent pipe.  Or a vent that does not vent clearly to the out of doors.  Check out the vent pipe first.  Make sure that it is clear all the way with no restrictions or reductions. Make sure that it is as straight and short as possible.  When you put your hand on the air flow outside at the vent cap you should feel a hard pressing column of air.  Without lots of air movement, you just can't dry clothes.