If you wanted to be even more accurate, you'd also have to take into account that most tasks are executed on the E cores, so having more of those, or faster, will have a much greater impact than any improvement on the P cores. It's impossible to estimate the impact like this - which is why Apple's performance claims[1] are based on real-world tests using common software for different workloads.

In summary, there is supposedly improvement in all areas so the reduced P core count doesn't seem to be a downgrade in any form as the OP suggested.

[1] https://www.apple.com/nl/macbook-pro/