Could you define/explain what you mean by "efficiency"?
GUE teaches also flutter kicking, but indeed the focus is not on diving with strong currents and potentially different procedures and tools might be needed (for example DPVs).
To my limited experience, in all drift dives I have done and with currents high enough to force the captain execute maneuvers to catch some of the divers I found no issue with my jetfins, but for sure they might not be enough for the currents you are describing. All in all, GUE-F, as stated in the class description trains people on basic skill refinement from OW and AOW level, and optionally (drysuit, doubles, canister light). Nothing more, nothing less. I would like to argue that potentially diving in high currents necessitate skills and tools beyond that skope, as also ice diving, etc.
Some GUE instructors are also free diving instructors themselves, thus I am confident that I good chunk of them already knows the pros and cons of different fins and they could potentially give their takes on the appropriate fins in different situations, which ofc is beyond the scope of GUE training.
I am not sure how standardized procedures and propulsion is disproved as a universal concept by this argument. Standards could (and do) necessitate different procedures and tools for different type of dives within GUE or other organizations/agencies with similar emphasis on standards. To the best of my limited knowledge, GUE doesn't have procedures (yet at least) for diving in rivers, or high currents, etc, because it's not the target environment of the agency for conservation or exploration. On the other hand they have procedures (I assume) for cave diving against currents, which objectively have no trouble executing safely using jetfins, or other equivalent fins.
Could you also define what you mean by efficiency here?
Both look very streamlined for the amount of gear they need to carry. I am not sure about the value of such comparison. It seems to me that the 2 people in the picture have COMPLETELY DIFFERENT objectives and definitions of efficiency, which results into completely different equipment, procedures, and mentality.
In your opinion, where is the commonality providing a common frame that would validate such comparison?
You got the point...
Efficiency is defined as the ratio between the distance traveled (in meters) and the energy spent (in Joules), as a function of speed.
For a given diver, using a given set of fins and kicking style, efficiency usually shows a bell-shaped curve, peaking at an "optimal" speed.
Short and rigid fins (such as the Scubapro version of the Jetfin, in which the original Venturi boost has been almost entirely removed), with frog-style kicking, usually have a good efficiency at slow speed.
Flexible, longer fins (such as the original Beuchat Jetfins or the Mares Avanti 4) and flutter kicking provide higher efficiency and higher optimal speed.
Competition-style monofins have low efficiency, but their optimal speed is very large.
Deep free divers use very long and very flexible carbon fiber fins or monofins, employing dolphin-style kicking, which provide the ultimate efficiency at medium speed.
Different fins and different kicking styles for different tasks....
But it must be understood that in the efficiency-speed curve there is a third factor, which is the human factor: geometry of legs and articulations, muscular strength, capability of sustaining a prolonged effort, capability of controlling motion, attitude and hydrodynamic asset, etc.
In a finned swimming course the instructor and the student performs a number of tests, with the goal of finding the optimal fins for the subject, and the optimal kicking pattern.
It takes MONTHS, in some cases YEARS to refine a finned swimmer. During this long period the muscles grow stronger, the motion control improves, and hence the diver needs to change fins two or three times (generally going towards longer and/or stiffer fins, providing more energy transfer).
My experience as a finned swimming instructor was entirely club-based and not-profit.
I followed some students for many years, seeing their slow but continuous improvement.
This is entirely unfeasible in the world of professional instructors and for-profit teaching agencies.
After doing this for 5 years I stepped to become a "pro", working in holidays resorts.
I had to change from 6-months courses to 6-days courses.
Here I appreciated the benefit of standardisation over personalisation. Using standard equipment is just one ingredient: what matters is to create a standardised diving system, with standard procedures, standard skills, standard planning, standard thinking!
This is both safer and easier.
A standardised diver can be stupid, and still be safe!
But having seen before the much higher efficiency, speed and performance obtainable with not-standard tools and methods, I feel to be correct to explain which are the limits inherent in adopting a standardised approach.
Among the various standardised methods, GUE emerges as one requiring very strict compliance, providing specialised and optimised approach to a set of very specific requirements for tech diving as a member of a team in caves, wrecks, etc..
But these methods and standards cannot be optimal ALWAYS. In some environments or for some specific tasks the optimal solution is different.
In my opinion a good diver should possess both the discipline and knowledge for complying with the standardised diving approach, but also the freedom and fantasy required for developing "heretic" methods to be used in out-of-standard situations.
In some cases I was the DM who had to solve issues with customers who were rigid in their compliance to standards, not realising that they were in a completely different new environment, which required a different approach.
So I repeat my suggestion to the OP: it is very good to be trained within an highly standardised "system" such as GUE. But one should keep control of his choices, adapting them to the actual needs, which in some selected cases can require to behave differently from the standard.