The damage any monster can do has the same cap. Though you can use the trait Hit Squad to break this barrier. Hit Squad will allow you to divide your hit, and therfore damage, into multiple hits each with the same cap. Then we'll use the other trait called Psycho to make every hit do damage a multiple times stronger than usual (I think it's about 2-3 times stronger)
A monster that can easily achieve this would be Conklave XY since he has both traits, Psycho and Hit Squad. To obtain him you need:
-4 Conklave level 20 or higher -Combine these to obtain 2 Conklave X -Have the Conclave X's level reach 50 or higher and combine them. -The result will be a Rank S Conclave XY with incredible stats. -Repeat until you have three.
Now when you get them you go into battle, increase your tension all the way too 100 (it only takes 4 turns)and just scout normally. The results (if you max their attack) will be a minimum of 4 times more what your strongest monster are able to do.
PS: Since metal monsters run away you'll have to farm meddle simes in Treepidition or Doubtback. Thy'll turn into metal slimes after you scout them and from there on just breed them to reach the upper metal mosters.
At the start of Treepidation, the first area in the game you can find a monster called a Meddle Slime. They look just like a Metal Slime but give less experience. They are a monster that you can scout. Heres the best part. When you do scout them they turn into a Metal Slime. Because of this the recruitment rate on them never goes down allowing you to get as many as you want.
Metal Tickets allow you to open up a new area called Metal Menagerie for a short time. Though on the map the location will how up as ???. This area is filled with metal slimes which give extra experience. There are a few ways to get this item. One way is to get them is through the blue chests. The blue treasure chests restock themselves so check them often. Monsters also drop them, so get someone with the trait lootest in your party it'll increase your chances of an item being dropped. I find Hunter Mech drop Metal tickets a lot.