Dungeons and Dragons

Not really sure what to do about this situation. I have a group that meets monthly. We do a lot of roleplay, but a few of my players are very into being OP at combat. They want to build their characters the strongest and the best. So I alternatively get requests to both break rules and strictly apply rules so they'll get advantages. They've also said they want deadly combat.

Not really sure how to handle this since their requests swing back and forth between RAW and not RAW. I'm finding myself saying "I want to follow RAW here" one day and then "I don't want to follow RAW that closely" the other day. They are in many ways kind of ruining combat for themselves as we aren't a wargaming table. We also have so little playtime I can't devote an hour or more getting into wargaming combat with them. It wouldn't be fun for a few of the other players (or for me) to devote our sessions almost entirely to combat and we usually have a few combats to get through.

As DM I feel pressured to be the cool DM and meet their expectations, but I'm also getting frustrated by the constant asks that boil down to wanting to be the most OP. I get the want, but it's getting to the point where we are having a running issue where the OP players don't want other players to do things for RP reasons and I haven't figured how to have this talk to halt the OP train here. The OP players basically want to enter combat, always hit with their attacks, have the max possible attacks and crits, never get hit back, just have the enemy stand there and take damage. Which is obviously a problem as that's terrible and boring combat.

The players in question are great people. They do roleplay, assist other players and contribute OOC. They do also agree it's my decision to run the game how I want. I'm just not sure how to express to them they need to slow their roll in trying to be a level 20 god at level 3.