I can't see him enter the tournament. As you said, they're really hammering home the plot point that the MC is less a hammer and more a scalpel. In the back. Less Luna and more.... calculating. Putting himself in (or simply participating by being forced) would ruin all that because certainly it seems even the MC knows his main strength is being under estimated. If you bring home the gold, no one's gonna wanna go up against you.
It's actually somewhat refreshing. He's a character who recognises his limits, and works within that to come out on top. It's not simply a game where you're left in command of a positive Deity amongst men (apart from his obvious big dick energy which makes the women love him but I suppose it's hard getting away from that)
Well, Hopes (the dev) has said that the Frenetico Tournament will definitely be coming in the future.
The tournament has already been referenced twice now, once by Luna and Gracie during the beach prison event, and now by Eiza during the "Unofficial Boss" event.
So I actually do see him entering the tournament tbh (despite him saying "No thanks" in beach prison event lol).
The tournament itself is a huge sporting event that is very popular in the underworld (in the DeLucaVerse, according to Hopes), and it really wouldn't make sense for MC to play a passive role and remain as a spectator.
Participation, yes. No idea whether he wins the tournament or not, but I think he may actually surprise a lot of folks despite his intentions by doing better than what everyone expected of him.
Cause whether MC likes it or not, he's already getting to the point where he's close to getting promotion to another rank (i.e. Elite Soldato).
Also, entering the tournament gives opportunity for the MC to earn rare weapons/equipment and money etc as prizes/rewards as stated in the beach prison event, so it also makes sense gameplay-wise.