It's FUD spread by people that hate that the xbox division isn't dead and buried. Fanboyism. Console wars. Nothing more. It's ridiculous that it's still allowed on this forum.
Why people have to turn things into extremes? like it is either huge differences, or no differences at all?
Nope, it is just the reality, that the more you have platforms to develop & test, less resources you have for one invividual platform. Devs dont have infinite resources.
We also have to think it as potential differences, which means that it can affect things, but it is variable thing as in holding back doesnt probably mean big differences, but it could also mean it, or maybe there isnt any differences that we can notice.
Situation A:
You have one system to develop games for -> 100 % of resources are in your reach to use for this one version.
Situation B:
You have 2 systems to develop games for
system 1 = relative performance is 100/100
system 2 = relative performance is 50/100
Even if they have same architechture, APIs and so on, you will probably dont have 100 % of resources to use for system 1, because some amount must be used to optimize&test for system 2 too.
Situation C:
You have 3 systems to develop games for
system 1 = relative performance is 100/100
system 2 = relative performance is 50/100
system 3 = relative performance is 40-500/100 (all the pc platforms)
Now you have to spare some resources to the 2 console versions + PC version, which means less time + resources for one invividual system.
So, either you have less time, money and resources per system, or you have to have more money and devs vs just having one system.
Anybody whom claims that there is zero difference between making game for 1 platform vs multiple is just using extreme ends wrongly.
Then there is the situation where devs would make game for PS5 only, and port it for pc 2-4 years later -> in this situation, assuming the PS5 version were made only thinking about PS5, PC version wont affect the PS5 version.
The real point is, that how do we define "it is holding back"?
Does it mean that it takes more time, or game isnt as pretty, or it is not as optimized, or there is anything different?
Fact is, that having multiple systems includes the potential to have something less, vs having only one system. <-- and this doesnt mean that all games are "held back", dont read it like it. It means that there can be potentially situations like that.
Also, if devs choose to do games using "100%" of series x potential without caring limitations of series s, then it kind of means that series x is "holding front?" series s version, if even after downgrades it wont be a good experience on sxs.
If devs have budget to combat against added cost to dev for multiple systems, then we can get the same results, if they have limited budget then we can potentially get something held back because of these limitations.
I own PS5 + SXS, and I personally dislike that devs have to make games for slower systems (sxs + ps4 + slow pc setups), but I understand that it must be done financially.