That's true of the ones that have only one hose to the outside. Those with two hoses are much better, especially if you insulate the hoses:
If we go by the DOE SACC ratings, this single-hose toshiba [0] has a 14% higher SACC rating than this dual hose whynter [1], for the same BTU/hr rating. If we go by the wattage ratings (note: these are usually peak rather than average), the toshiba does use 13% more power than the whynter, so let's assume it cancels out and they both have the same energy efficiency. The toshiba is still $144 cheaper than the whynter. That's hard to justify for "dual hoses seem like they should be more efficient" without any actual evidence.
Please prove me wrong, before it's too late for me to return the single-hose one.
[0] https://www.toshiba-lifestyle.com/us/Room-Air-Conditioners/P...
[1] https://www.whynter.com/product/whynter-elite-12000-btu-dual...
The dual hose unit will likely outperform significantly if the temperature delta is high, but if the temp delta is low then the single-hose unit is probably better as it likely has a more efficient compressor.
It looks like DOE SACC tests assume the outdoor air temp is 83 degrees for 80% of your usage and 95 degrees for 20% of your usage.
In case anyone is interested, I did not end up returning my single-hose unit, but I did end up buying a dual-hose Whynter ARC-122DHP [0] for another room. It came with a yellow energy guide card listing a cooling capacity of 12000 BTUs and an EER of 11.1, which indicates an average power draw of just 1081 watts (EER=BTU/watt). Unfortunately no SACC or CEER rating was listed. Actually measuring power shows that it draws the full 1200 watts on startup, quickly drops to around 1100 watts, and then slowly drops to 900 watts as the room temperature falls. For comparison, my 8000 BTU (unknown EER, 6000 SACC, 6.5 CEER) single-hose Toshiba RAC-PD0812CRRU [1] also draws 1200 watts on startup, quickly drops to around 900 watts, and then slowly drops to 800 watts as the room temperature falls. So it seems like the dual-hose is around 20-30% more efficient (in a different room under arbitrary conditions) based off the BTU rating, but no better based off the SACC rating. I also noticed that it did not come with foam seals for the window bar like the single-hose unit did, so there is probably room for some efficiency gain there.
[0] https://www.whynter.com/product/whynter-elite-12000-btu-dual...
[1] https://www.toshiba-lifestyle.com/us/Room-Air-Conditioners/P...
That air has to come from somewhere, so it's going to pull warm air from everywhere it can, door, windows, any creaks/holes/openings, etc. And the fans have some serious airflow/CFM.
Dual hose designs pull air from outside and expel it back outside.
So technically it should be capable of getting your room colder and keeping it that way with less compressor usage.
The cold part of the A/C just circulates air around the room on any model.
Looking at my model, I could turn it into a dual hose design - it pulls air from the rear, right below the exhaust vent. That seems to be the case for a lot of these. Creating an attachment/adapter to connect another hose seems easy enough.
I went years without any AC and my bedroom wall faces south. My room would get so hot in the summer I couldn't get any sleep. Tried an evaporative cooling unit because they're cheap which did absolutely nothing for me. Eventually broke down and got a portable AC which unfortunately was a single hose unit. You really need to look carefully at what you're buying because the whole single/dual tube thing doesn't seem to be something the sellers put out there. Even though it it was a single it still made a world of difference. On really hot days it doesn't get super cold but cool enough that I don't notice the heat.