The reasons you gave only took into consideration the difference in time of a small change, (pushing either comma or dot with one thumb, and doing the next in the sequence with other thumb in a far away location vs doing it with the same thumb when its close) and didnt at all touch on what makes it so inefficient.
You are saying its two thumbs over one, when that isnt the case. You are not typing
an amount or buttons in the combo, you are typing the combo as a sequence.
Using both thumbs is splitting up what one thumb can do in a naturally following sequence to do it with two, which also ties the other thumb at the worst possible place.
You cant pause time, if both are comparativly fast, you wont have extra time to move the left thumb away from worst position.
Either you are fast at pressing comma space, or you have tought yourself to press comma space fast. One is just better for all, and familiar, the other takes skill.
If you are saying the actual from comma and dot to something else is as close to instant as possible, that means you pause time at the difference between the two, lets say its the same.
The time you have to react to get left thumb away from worst position when its typing comma or dot, is worse than the same time you have to move left thumb being at away from
ideal position if its doing neither.
Consider what happens when your shift+ sentence starts with T.
In one scenario you have to move from bottom left, all over to T, in the other, you have time to move from D or F (where your thumb naturally hovers) over to T while you are busy with the other thumb.
Unless you are moving your right thumb over to do it and you are _really slow_, much slower than you would be moving in a swipe-combo, then you see the point.
And its not like you then arent tied up where you shouldnt be.
Again, its not a case of x amount of keypresses divided by each thumb, thats not how it works. You are then making the argument each thumb has a fixed apm, which would be true if movement wasnt different between keypresses.
Clusters of keys often used, close together is what makes a keyboard efficient, mathematically. You shift neither focus, nor do you travel an extra distance. That also pans out for novice users.
You are mistaken about QWERTY keyboards. Its a layout to prevent locking, which is only secondarily what makes it less efficient.
"gummy" and "lament" over and over again is probably as far from a practical use-case as you can get.
The scenario is very limited. It doesnt take into consideration that you either can or cant type other letters than A-Z (äöÊüøæå etc) This is the one real difference a full layout makes. Measured both in familiarity and speed.
And you arent considering placement of comma and dot, space, enter or shift. Which is the other option that can be made.
At least make it "Lament. shift" "Lament. enter" or "Lament, " And then start your sentence with A-Z+whatever else.
In the long term I don't think it will be a huge problem, just an inconvenience when switching between the Pyra and a real keyboard.
This is sub-par behavior. It is not as good as avoiding it.
Edit: The reason why comma dot on the right makes sense, is the exact same reason shift on the left doesnt. Try it.