Honestly im not the type to care about age gap but i still not shipping him with mc.
And If eunhan never ask the spirit, i still think he would keep liking mc, cause he is more or so mc obsessive fans. From how manipulative he is, hangyul will still endup with him. They meet since childhood and work at the same industry so that possible for them to be in relationship, maybe until hangyul meet his real partner.
And for the gangster he would still be a debt collector and still not liking mc cause he will be more interested in mc brother (i think he more interested in someone who dont show interested in him, like mc brother who hate him) but hangyul will definitely falling for the gangster just like the original plot, and maybe the gangster will feels a annoyed at eunhan for taking his fated partner so he will also ruin mc and eunhan relationship just for his own satisfaction.
I know people are saying that its weird that heewon is after hangyul (since he met him when he was in high school) and I agree with that 100% but I think what yall forgetting is that he is the fated person for hangyul so my guess is if eunhan didnt manipulate fate, heewon wouldn't have met hangyul under that circumstances especially being their debt collector since this was all the spirits doing. I am guessing he would have meet him somewhere when hangyul is a successful adult actor and from what it looks like my guess for their age gap is 6-7 years.