Sorry for not answering earlier, I was on holidays and didn't read the forum. Also sorry for sounding too arrogant. My bad.
The cars do suffer a lot from understeering but they somehow managed to cope with it with suspension geometry and diff ramp angles. If you remember the 2011 WRC cars were being driven ridiculously sideways on the loose surface at their beginnings. The reason for that was the abscence of the center differential.
I don't have exact statiastics but when the gr.N 4WD cars were still a thing (unlike today) the far majority of tragic accidents happened with them. I can name a lot of them from my head but I don't think it is necessary. Only here in Czechia we had more than 10 dead from gr.N accidents (most of them spectators). In most cases the reason was the same - uncontrolled rebound of the powered rear axle which was caused mainly by too short suspension travel. Simply said bouncing cars are always spectacular but also always dangerous.
Several examples of the uncontrolled rear axle rebound after a short youtube search.
https://www.youtube.com/watch?v=kF9WuVrd8so (this one ended tragically for one spectactor)
https://www.youtube.com/watch?v=J3Ocf5KwVr0
https://www.youtube.com/watch?v=8SOeOa13ypo
https://www.youtube.com/watch?v=2gb0dmFdUAQ
https://youtu.be/9Wj-WX-h5B4?t=199 (not an accident but an extreme case of a gr.N car with very short rear axle travel, in this case the rear axle was not driven so it could not cause a spin)
No, I am sorry but it isn't that easy. 2011 WRC cars and R5/Rally2 cars have the same turbo boost but also different restrictor size and often also different bore/stroke ratio. The WRC cars had the peak power in higher RPM than the R5/Rally2 have because there was enough air for feeding the engine in high rews. The R5/Rally2 have relatively flatter power band because they run out of air quickly. Simply said from the peak power to the RPM limiter the power is relatively constant because it is limited by the restrictor and the R5/Rally2 achieve the peak power about 1000-2000 RPM earlier.
It didn't go well in terms of reliability and I wrote about that. The problems had nothing to do with the performance.