The opposite is true, it is a must that this data is added to these items. For a sports season it is basic information to have the sport in question being added, as otherwise these items are practically useless. The opposite is their purpose: to be useful. One of the first things users of the data want to do is to be able to select the sport in question data is wanted from. Commonly not all sports at once but one single sport, let's say football, tennis, baseball, ...
On top of this would adding the sport also help to make these items even extra useful: most of these items have only one or two statements on them. By being able to select the sport, the users who work with this data can better focus on the items for that particular sport those users are focussed on.
Two months ago I published an analysis in what became clear that the stability, quality, and inter-item structured data is far from the structured level as what in general would have wished for and would have expected. Wikidata contains structured data, but only on the level of a single item. In practise, structured data goes beyond just the single item and is needed on all levels of data. Sadly it is missing on the various levels, which makes it for individual items not a good to just say that we need to rely on the data on other items. In closed data systems there is a structural coordination in place, which takes care of structural adding of data on all levels. There it is possible to rely on relationships. Wikidata with its open nature misses the structural coordination, and misses the structured data beyond the single item. And as those (missing) levels define the relationships, it is not something to reply on.
To continue, on Wikipedia (and other platforms) the communities have set some standards to make sure that the content has/gets the minimal quality. For a large parts the quality of the Wikidata just sucks, often it is almost completely missing, incomplete, inconsistent or even false. With luck, a dedicated contributor has taken great care of a relative small group of items, but large parts are a big mess. I remember from 15-20 years ago on Wikipedia people saying not wanting to have basic standards, like for example as that was considered redundant, not needed, etc. By now most contributors have hopefully learned how wrong that idea was. I am sorry to say, but that is what I see happen here too.
We need to get to basic standards for sport seasons items. Besides indicating that it is a sports season (P31), other basic properties that should always be present are country, sport, point in time, sport season of, follows, followed by.
With today's challenge, the focus is first the sports. On this users can build further to get that all sport seasons have at least the basic properties added.
Romaine