The biggest issue here is the presence of long-standing employees who rely on seniority rather than competence. They are resistant to change and have created a vicious gossip culture.
If you are efficient and finish your work quickly, you become a target. Instead of valuing productivity, the "old seafood" clique gossips behind your back, making snide remarks that you "have nothing to do" or are "slacking off." They equate time spent in the chair with hard work, completely ignoring actual output.
There is a serious cultural problem regarding working hours. I have witnessed highly efficient colleagues complete their tasks and leave on time. However, instead of being praised for their time management, they are shamed by the gossipers for "leaving early."
The reality is they finished their work—they are simply not buying into the toxic mindset that you must stay late to look busy. The people who stay behind usually aren't working harder; they are just slower, or they are lingering to create a false impression of dedication. The office confuses efficiency with laziness, and presenteeism with commitment.
This is a terrible environment for anyone who actually wants to get things done. Talented people leave because they are tired of being talked about for leaving on time after completing a full day's work. If management doesn't start valuing output over hours spent loitering in the office, the talent drain will continue.