I am certainly not an expert, but I have had some success in rental (hire) karts as well as 4-stroke racing karts.
My main question for you is what does the kart feel like? If you put just a little more steering in, will the back start to slide? Or does it just plow straight ahead no matter what you do? I certainly understand your concern about not being able to unload the inside rear tire and agree that it’s an important thing to be aware of. However, it may not be as big of an issue in some rental karts, at some tracks. Different tracks, or even just different karts at the same track can have wildly different handling. If the kart is somewhat balanced and the rear will start to slide if you turn the wheel more, then I would not be concerned with altering your line in a long sweeper.
Some thoughts about lifting the inside rear tire: to me, it is easier to notice with soft racing kart tires than it is with rock hard rental kart tires. However, with that said, a very tiny amount of steering input may bog down a rental kart significantly, while a normal amount of steering to get around a corner may unload the inside enough to reduce the drag. While this is unproven, I think in some rental karts, in some corners, it can help to be either at “full steering lock” (the max steering you normally get to in the corner) or perfectly straight ahead. No in between. Either unload the inside rear tire as much as possible, or set it down all the way and drive straight. I think you were already kind of thinking about it this way. The main place I think this thought process can help is long sweeping exits, where you can keep turning just a little longer, and then go completely straight to the next corner entry.
In some cases with rental karts I have found unconventional lines to be faster, but not in the way you’re talking about. With such a lack of power, sometimes it can be faster to really try to make the track as short as possible. Not only does this include simply running on the inside of the sweeper for the full length of the corner, but also not using the full width of the track on exit.
I do have an example, which is the closest thing to your suggestion of driving in two straight lines with a sharp turn in the middle. It was not a long sweeper though, but two corners that basically became a double apex corner. Outside of the track, there was a concrete runoff area. In rental karts, in the rain, on slick tires, you could drive into the corner very straight and go off onto the concrete area, suddenly have grip so you could turn, and then get back on the track and drive a relatively straight exit. I have never encountered such a situation in dry conditions in any kart.
So I guess what I am saying is, there is probably not a benefit to what you are suggesting.