And, because you already brought up the example of the statues of prominent slave industry figures like Colston, there are several key differences between that example and this.
Firstly, the context of a statue is that it is put up to commemorate and celebrate an individual person. The most similar type of painting would be a portrait. This is not a portrait - it’s a landscape with figures. They are, so far as we know, anonymous. It may have been based on a real life scene, or it may have been entirely from the artist’s imagination. Given it’s not commemorative of anything, it’s harder to distill what about the picture is objectionable, particularly if it’s depicting a real life scene.
Secondly - the activities of a figure like Colston that are being celebrated by the statue are established fact. Here, you are replying entirely on assumptions in order to construct a narrative that the painting represents a slave. Against that, the boy is dressed in expensive clothing, is literally front and centre of the picture - he is not in the background, or “set dressing” - and if a real figure, was living in a time where it is more likely than not that he is a servant, not a slave. Your assumptions may differ - that is fine, but that illustrates the point - we are dealing with subjective assumptions here, not objective facts.
Thirdly, as we’ve already discussed, an art work like this will have an inherent value that statues tend not to have, based on the identity of the artist (it’s very rare that anyone values a statue of a historic figure based on who the sculptor was) and its value as a contemporaneous image of the past. Again, a statue of a dead white man created after his death doesn’t have this aspect that might cause it to have value. The painting may not be to your taste - I am not fond of the works of Lucien Freud, for example - but it as be foolish to think they aren’t highly valued by others.
So, to my mind, this is not the same kind of situation at all.