How is it a bad port?
NXGamer says the Xbox ports are excellent; PS5 version is a tad better likely due to higher clocks (better fillrate for this title), and more experience with an engine already running on Playstation for many years. It's not like the performance of MLB the Show is out of the ordinary - most third party games run better on PS5. So maybe it's down to technical reasons for why the perfomance is better, not any kind of technical sabotage like you are claiming.
First, to say that most multiplatform games work better on PS5 is a fallacy... In fact, the data says the opposite even when the general rule is equality. But OK, it's your narrative.
Then, calling a version excelent port in which you sometimes offer 20-25% less performance when that is light years away from the general norm of what is seen between the two consoles and also being a crossgen sports game.... Is a massive joke. If you add to that the fact that the XSS version becomes even lower in performance and options than that of PS4Pro.....
The question, is MLB premeditated to favor the PS5 version...?
It happens that it is SONY itself that initiates the suspicion (which also reaches the multiplatform games with which it has a marketing agreement) when it accuses MS of being able to consciously downgrade o sabotage the PS5 version of COD.
If in the next COD XSX becomes the base development platform, logically that will favor having the most polished version with the best performance... If that is the normal tonic and it is accepted... why are Sony accusing? Is it sabotage when XSX favors being the base platform for development??
So much concern in the comparisons of DF and VGtech makes it naive to think that SONY does not provide the means for the studios to favor the PS5 version over the XSX version when signing marketing agreements for example.
That in later patches the XSX version is improved? Precisely Sony also complains about that possibility for PS5 versions.
Sony believes that the damage is done at launch. It doesn't matter if later patches fix it, for them only the result at launch matters. Here, Sony is declaring a kind of self-granted right whereby parity only takes place when PS5 is the base development platform and the most polished and anything that is a better version of XSX is unacceptable and irreparable damage to the image. and PlayStation prestige

In summary, when Sony accuses and points out, it is not only being hypocritical and showing desperation... it is also exposing itself and leaving the door wide open for people to think that it is worried because it is something that it already does but they don't want to suffer.