[imported_luckyme]

Pretending I know what your terms mean (added lettering to your statements for reference)-

[ QUOTE ]
-(A) All similarities between things are merely concepts
- (B) All concepts about things are merely constructs from our mind, despite whether or not they correlate with the reality of particulars
- (C) All things are particulars

[/ QUOTE ]

If B is true, then A seems an overstatement. At the least, the concept of similarity is not about things but about the the concepts we have of them. So, those times when the concepts do correlate to the reality of particulars the similarity will be an actuality, regardless of whether the concepts reflect the particulars in any meaningful way.