Although storylines between themselves are way too different, the design between each lead is in familiarity
From Big Bet, there's an articulate casino lead manager/founder along the way within the Philippines, alongside a right-man and clueless-but-follow-by-the-book & first-abroad-experience police inspector; whereas from Decoy, there's a bluff-but-dangerous con artist 'king' and ex-lawyer-turned-detective, which his traits turned out to calm-while-collect-thoughts and no biased judgment (put personal feelings aside for professionalism)
and the methods are quite similar to male leads themselves: Cha Moosik has his own influence right from the start (childhood, which is enormous), hence being eloquent, and full of pride to be communicated with all people; whereas Noh Sangcheon convinces his people and also, 'baits' aka victims, to believe his encouragements to buy the products on his pyramid-scheme journey
If you want to watch these Korean dramas, I'd suggest to binge-watch all of them, don't be like me (wait each week); so for Big Bet, start within the middle of March because that's when all eps from the sequel are finished; whereas for Decoy, mayhaps at the end of April for other 6eps of the sequel to finish
Decoy: Part 1 (2023)
Similars
Both have the same level of mystery and twists within the Police Force. Both are stories of detectives chasing after the truth behind an unsolved crime, that took place in the past, through cases that take place in the present.
Both dramas revolve around about a complex case that connects every character and spams over multiple years. Both dramas are mystery, at times gritty and artsy dramas dealing around corruption.
Both detectives leading the investigations are independently rich (bringing interesting workplace dynamics), Elijah is in both of them (I thought it was just someone looking a lot like her, LOL, initially, nope, same actress), both MLs (of the two dramas) have colourful past experiences and things to clear up. Also, both MLs are definitely smart and tend to notice small details (which is always a plus.)
TGD had a pair of detectives, it looks like Bait/Decoy won't.
Depending on how Bait/Decoy develops, it might turn more noir than TGD ended up.