I know the MPGs take a significant hit in the winter. It's been 23 f here and my hwy mpg has gone from 40 mpg in Sept to 30 mpg now in my 2023 RAV4 hybrid. My V8 4Runner only lost about 2 MPGs in the winter.
Assuming your V8 4Runner was normally around 16mpg, a 2mpg drop is 12.5%. Going from 40mpg to 30mpg in the Rav4 is a 25% reduction. Most likely the reason for the bigger drop in the hybrid is the fact that hot engine coolant is used to heat the cabin. In order to keep the coolant temps up, the engine probably has to run more in the winter than it normally would, thus the larger dip in gas mileage.
The Rav4 parallel hybrid system saves fuel because it is really aggressive in kicking the engine off and the electric motors do all the work at start stop unless you are really leaning into the throttle. If it can't kick the engine off, it can't save as much fuel.
I expect the efficiency difference in the 1 motor style hybrid from Tundra and Sequoia is smaller than 25% in the winter. That system very much seems to keep the engine running and instead using the electric motor to blend between low load and higher load situations which lets the engine run at a more efficient load condition. That's also why it doesn't seem to see the efficiency bump that the systems used in Toyota's transverse hybrids. It's a slightly different approach for a different buyer segment.
When the Lexus GX 550h comes out with the 2.4T hybrid we will get a really apples to apples comparison between the V6TT and 2.4T from a performance and efficiency perspective. As it stands, the hybrid in the Tundra, Tacoma, Sequoia, 4Runner, and Land Cruiser is there for a performance bump with no efficiency hit versus keeping performance the same and looking for more efficiency. Toyota has addressed the complaints about sluggish performance. They haven't built a version of their body on frame trucks that is OK with "5th gen 4Runner performance" but wants efficiency on par with a Highlander.
The Grand Highlander is a neat case where they offer the 2.5 hybrid (mid 30s gas mileage, low 8 0-60), 2.4T (high 20s gas mileage, low 8 0-60), and 2.4T hybrid (high 20s gas mileage, mid 5s to 60). They cover all the use cases. On the Tacoma and 4Runner, it seems like we will get only the choice of OK performance or High performance and both versions will get just OK gas mileage. That said, maybe that's the right call from a business perspective. There may not be many buyers that are OK with 250hp in a 4Runner that can manage 28mpg.