Well, it doesn't reallly matter which terms you use to classify these independent aspects of pieces. In orthodox Chess they will always be synonyms, as the Bishop and Knight fall in one group, and the Queen and Rook in the other. Weak and Strong can also be used interchangeably with major and minor. The point is that it is different in chess variants, so what will be synonyms for orthodox Chess, can describe entirely different concepts in variants.
I'd note that using 'strong minor piece' or 'weak major piece', as I did, might be seen as removing ambiguity over what is meant. However, if one prefers to use just one word/aspect, instead of two, then using 'heavy piece' and 'light piece' (rather than being 'more specific', or in other words have more categories, e.g. using heavy minor piece, light major piece, or heavy major piece, for example) might be seen as also unambiguous, as long as it's agreed by [ideally standard] convention that this is in the context of chess variants, rather than for orthodox chess.
I'd note that using 'strong minor piece' or 'weak major piece', as I did, might be seen as removing ambiguity over what is meant. However, if one prefers to use just one word/aspect, instead of two, then using 'heavy piece' and 'light piece' (rather than being 'more specific', or in other words have more categories, e.g. using heavy minor piece, light major piece, or heavy major piece, for example) might be seen as also unambiguous, as long as it's agreed by [ideally standard] convention that this is in the context of chess variants, rather than for orthodox chess.