Nobie
, The reasons why 1111 Mii Brawler's strengths aren't discussed that much is because the character has been overrated for so long. It took over a year for people to realize that 1111 Brawler is one of the worst characters in the game even though the best Brawler player at the time was saying that 1111 Brawler was one of the worst characters in the game (Dapuffster is probably the best Brawler player, but Yikarur has been putting up the most results as of right now). Most people realized that 1111 Brawler has good mobility and combos, but they didn't realize that 1111 Brawler has poor killing ability and poor landing options. Even now, ZeRo and the Smashwiki forget that Mii Brawler has trouble taking stocks, and they overrate the character. 1111 Mii Brawler's situation is different from the other Miis because Brawler is the only Mii Fighter that gets overrated.
Only 4 moves kill at reasonable percents for 1111 Brawler, and he/she doesn't have a confirm into any of these laggy moves. While 1111 Brawler can use jab mixups and punishes on missed techs to land a killing move, the fact that Brawler has no safe way to get a kill at reasonable percents gives the character some of the worst killing options in the game. When this is combined with 1111 Brawler's poor range (Shot Put isn't that great in the neutral because it has slow startup, high endlag, and poor range for a projectile) and poor disadvantage state (1111 Brawler has poor recovery, and he/she has to rely on laggy, stall then fall moves and aerials with poor range to help the character land. The main redeeming quality of 1111 Brawler's disadvantage state is a combo breaker in nair) it makes 1111 Brawler one of the worst characters in the game. In addition, Brawler's poor aerial acceleration also hinders the character's approach.
To sum up the previous paragraph, 1111 Mii Brawler has major weaknesses in the neutral, advantage, and disadvantage states that makes the character a poor choice for competitive play. While 1111 Brawler has strengths, the character is completely invalidated in competitive play by Mario (Mario is better than 1111 Brawler in every state of the game, and Mario is easier to play. The fact that the two characters have a somewhat similar play style makes the issue worse). This is part of the reason why 1111 Brawler has virtually no tournament representation.
The addition of Helicopter Kick and Feint Jump turns the weaknesses in the advantage and disadvantage states into strengths. The confirms into Helicopter Kick give Brawler the safe killing ability that the character needs for a great advantage state. Feint Jump gives Brawler the landing option and recovery option that Brawler needs for a very good disadvantage state.
1111 Gunner isn't in the same situation because Gunner has some tournament representation and skilled mains. Recently Wii Twerk Trainer got 5th in 2GG Breakthrough using Gunner as a secondary, and PK Offbeat won a local tournament using Mii Gunner with Kirby as a secondary. Flama is ranked second in his region in Mexico, and his results have improved since he was ranked 15th in all of Mexico. ROM doesn't attend many Japanese tournaments, but he has won sets against Kirihara and Daiki (he also won against Pugwest at Genesis 3). Since Flama is planning on attending some major tournaments next year such as EVO, there is hope that 1111 Gunner can rise on the tier list in the future. While Gunner's grenade, missile, and bomb drop can improve Gunner's combo game, conditioning, and landing options, it isn't as huge of a upgrade as Brawler's moves because 1111 Gunner's specials aren't that bad.
1111 Mii Swordfighter is among the worst characters in the game because the character has poor mobility, poor recovery, and killing issues (the character lacks confirms, but he/she has more killing options than 1111 Brawler). While Swordfighter has good range (it is not good for a sword fighter), a solid projectile in Gale Strike, decent combo ability, and a dair that isn't that bad of a landing option, the character has not gotten any results in a very long time. Chakram, Hero Spin and Reversal slash can improve Swordfighter's combo game, killing ability, recovery, and anti-zoning, they aren't as game changing as Brawler's moves because they aren't as good.
I'm not sure if the miis were designed to be bad characters, but most characters would look bad if they don't get much representation or development. Considering the fact that Miis aren't allowed in for glory and most of the tournaments in the tournament mode, I am not sure that Miis were designed for competitive play. I hope that this wall of text has answered all of your questions.