I can be! Tbh we can find similarities in dajeong and MC's personality so maybe he might have gone after him becuz of that.
But at the same time it's not like he didn't made a move on dajeong at all during this time becuz from the main story we could see that boss was having sex with dajeong at the same time when he was going after mc. All I know is that this man has some really fucked up logic ╥﹏╥
I don't remember the exact chapter but I remember that dajeong did appear in the main story. The boss was having sex with dajeong while imagining it was the mc. He also appeared in another scene too when he met the mc. So yeah I think that if mc really is a replacement then I highly doubt he would have acted like this in the main story and hurted dajeong like that

It kinda feels obvious that the boss is interested in dajeong, like the way he doesn't let him leave and he hinted at how he never saw him as a brother ( ̄ヘ ̄). Knowing how fucked up and twisted of a guy he is, I feel like maybe he is doing this (going after the mc) just for the fun of it and to "tease" dajeong (or basically any stupid reason like that)