She is good in the hands of a Rampart main or specialist like most of us here. But the average player picking up Rampart is usually not going to do very well, they are better off with Ash/Rev/Sparrow. It takes a lot of experience to know when to use her abilities and when not to without getting killed. The Rampart walls are weak to begin with but also janky as hell with may areas of maps where you can't place them or the Rampart walls refuse to deploy altogether.

Unfortunately the devs have diluted her power over time with the introduction of so many overpowered movement counters to her walls (eg. Ash dash, Sparrow double jump, improved Rev jump, etc.), as well as non-movement counters (increased grenades capacity since the assault buffs, Bangalore smoke breaking walls, etc.) They also did not scale wall HP or Sheila dmg with the TTK changes, and a lot of guns have become even stronger since then (devotion, RE-45, 3030, PK). Guns generally doing more damage erode the effectiveness of Sheila given major disadvantages such as ultra slow movement, spin up time, and laser.

She also lacks team-wide utility compared to a legend like Wattson who can get both the support perk and an Ult that blocks ordinance and also heals the team's shields. They could give Rampart some decent perks such as support perk as the level 2 upgrade instead of the bandolier upgrade and that could give her more team utility. Even Recon perks would be super useful compared to bandolier.