I'll go out on a limb and say it will. With how popular PS4 is and with Switch not being able to get third parties(that xb2/ps5) will, switch sales will prob stagnate. So I feel PS5 if going off PS4 success,will catch up quicker than anticipated
I am thinking with all the moves Microsoft has made they might be able to convince some people that would buy a PS5 might end up buying a xbox instead.
As for Switch stagnating it's definitely a possibility, i think it depends on how well Nintendo will be able to provide 1st and 2nd party software cause like you say 3rd party might be a lost cause.
Switch friend-code: 6700-1526-7903