I wonder if this problems will
Be solved with Cortez X3? Or we are going to have another generation os problems for next year?

At the end I understand that the X2 is very similar to the X1, just pumping more power to it to get better performance (like Intel does) at expense of battery life.

Switching to A710 only could be a solution in midrange (is the configuration of the MT Dimensity 8100) however will penalize single core performance (the whole purpose of the CorteX X series, compete with Apple in SC)

Any news on Cortex x3?

I think its more to do with Qualcomm's implementation over X2's design. Agreed that there is a big power draw with X2, but mediatek has managed it fairly well on TSMC 4nm node, so we know its possible. Frankly, i dont believe in underclocking the X2 as it beats the purpose of the ultra performance it offers. If that was the case, they could just drop the X2 in favour of 2 more A710 with a maxed freq with the following configuration (2XA710 max freq + 2 X A710 2.4Ghz + 4 X A510 1.8Ghz). The easiest method for Qualcomm to do would be to keep the X2 as it is, and drop the freq of A710 from 2.5Ghz to 2.4Ghz and take the benefit of 30% power savings from the generational jump of A78 to A710 for similar performance. That combined to the TSMC 4nm mode efficiency gains should gain them substantial improvements.

They should copy Apple A15 which target efficiency and then it's easier to add another core for more power like A15(pro).

It kinda makes sense since Mediatek Dimensity 9000 is also quite power hungry in the tests, even though it uses the same Cortex X2 and TSMC 4nm IPs, so unless Mediatek is doing something awfully wrong, the big culprit of this is the Cortex X2 IP. Frankly, the Cortex X2 high power draw isn't such a big surprise given it is a performance core. The biggest offender is the middle core, the A710 which isn't that much more efficient than the X2.