Fiberglass tape is used for convenience and quick construction in my opinion given the three longitudinal joints presented during construction in a four panel hull. Your assumption that the bottom panels are only stressed in one direction is valid if there is no vertical movement of the kayak and paddler as will occur in waves or while paddling. I would disagree that the interior bottom panel is under compression with a static load though. Given that the chines and keel aren't bending the resulting force supporting the kayak is UP and into the hull, Imagine how the skin on a skin frame looks, it bends in, therefore the interior skin is under tension. Which if one were set on glassing only one side it would be the interior. But given that the hulls aren't static pieces sitting on a mantle piece it's worth putting the glass where it's needed. I can tell you that the cocpit bottom panels on a Patuxent 17 I made 7yrs ago were full of lengthwise cracks even though the interior joints were layered with two (!) layers of 3" 9oz tape AS INSTRUCTED IN THE MANUALS with 6oz exterior glass. With rigid keel and chines the unglassed area in between allowed enough flexing to occur in moderately rough water use. Along those lines I picked up a Ch16 bare hull that had tape and cockpit glass. In the aft compartment where there was no cloth except the tape on the joints I could press down onto the exterior of the bottom panels BETWEEN the 3" tape and make the wood elicit cracking sounds. There's nothing wrong with making a four panel hull with only tape, cloth, or some combination thereof. It all depends upon the use, load in the kayak, size of the panels, whether the unglassed areas are large and exposed to direct forces (flat bottom, large areas), and angle of the bottom panels.

My experience has been that unglassed cockpit glass in a four panel hull will allow for enough flexing to open microscopic cracks and allow water instrusion. 4mm decks that aren't glassed will also allow enough flexing in hard use us allow microscopic cracks for water intrusion. It's not the end of the world and the wood can easily handle that kind of flexing and water intrusion.