Michael, I am going to respectfully disagree to a point. A lot of the following is for the wider audience as I realize you are intimately knowledgeable on these items, more so that myself, so correct where necessary.
It is lost time and honey to wax production and lost foraging due to lack of storage.
Honey consumed while secreting wax and building comb:
The lost time does equate to lost honey and not just lost foraging opportunity during flow. From literature, a colony of about 50,000 bees can secrete about ½ pound of wax per day. That equates to about 3 medium frames per day of wax. The bees that are secreting are doing just that and only that. The carbohydrates these bees burn during this period comes from consumed honey. This is where the 8 pounds per pound of wax is lost. Four pounds a day for consumption during comb building. It is my understanding that the hormone level in bees rise when their honey stomachs are full and this initiates wax secretion. Also foragers and just emerged bees are not the bees secreting wax. It is primarily the bees that are 2 or three weeks old.
Honey lost due to inadequate storage:
Three medium frames of wax hold about 12 pounds of ripened honey. Nectar weighs less. Most plant nectar is 40 to 50% sugar with the balance moisture with a few percentage points of other inclusions (these give different honeys different tastes). Therefore nectar requires greater storage volume. If you figure that nectar is 40% sugar/60 % and is dried down to 18% water(moisture content) then nectar conversion to honey changes the ratios from 40/60 to 82/18 sugar to water. 1 pound of nectar has 9 ounces of water in it and 7 ounces of sugar. 1 pound of honey (18%) has about 2.8 ounces of water remaining in it. So for every pound of ripened honey stored the bees collected 2 ½ pounds of nectar (more or less). So during a heavy flow when honey cannot be dried fast enough additional comb is needed to accommodate the wet nectar. About twice as much as for ripened honey. This allows for some ripening (moisture reduction) to occur during glow. This means that the bees in an average size colony (50,000) can generate enough comb per day to accommodate about 12 pounds of ripened nectar which should eventually yield about 5 pounds of honey. Using these numbers, if there is not comb available for storage, then the bees are limited to about 35 lbs of “surplus” honey per week production during a otherwise boundless nectar flow. These numbers are ballpark as there are few if any absolutes in beekeeping.
So as you say, there is certainly lost foraging due to no storage space during a heavy flow if there is not drawn comb available for use. I would be interested to know what actual field weight gains are from similarly populated Langstroth with drawn comb and a Top bar with no spare honey comb sitting side by side are during a short intense flow.
Also unconsidered above is flow timing and comb building:
The bees that produce the wax are generally 2 and 3 weeks old. If the flow is early, before the hive has a maximum supply of wax building bees, then they will not be able to produce enough wax to store the honey coming in. This results in additional loss of surplus due to not having drawn comb.
Hive configuration losses:
It has been mentioned that top entrances can increase honey production. This could be in part due to quick and close access of the storage areas to the house bees. Less distance the bees have to travel to store equates to more foraging time. More foraging time equates to more nectar. In a Langstroth hive with the standard bottom entrance, the bees can move from the bottom of the hive directly along many paths to the top of the hive. On a TBH they have to transit the entire brood next before reaching the storage area. This equates to lost foraging due to the foragers having to “wait” for the house bees for a longer period. I imagine that a TBH with a slot entrance on the side that can be adjusted as to the entrance position could be utilized to give the foragers and house bees quicker access to the storage areas. This may also reduce the swarm instinct by decreasing traffic through the brood areas.
All the above is academic to actual field experience. And mileage may vary. From my experience with my TBH and langs, the langs far out produce the TBH. My TBH produced about 20 pounds of surplus the first year. Second year about 10. I then added some lang supers to it and they filled up 2 supers (75# honey). My langs have all averaged 100# per year or better. I will have to qualify that a bit as the TBH was completely treatment free and yielded 2 splits and then swarmed in its second year. It doed out due to mites and SHB this past fall and I was glad to see it gone.
If you are not concerned about honey production and do not extract and are prepared for the extra management a TBH entails then it should be cheaper to get started with. Mine was more frustration than it was worth