Stupak credits Fedorov with achieving something no-one would have imagined possible ten years ago: dragging the sclerotic, rigidly inflexible military into the digital world.
In his short time at the Ministry of Defence (he was only appointed in January), Fedorov pulled off a number of coups, including persuading Elon Musk to block Russian access to his Starlink satellite-based internet service.
The move is thought to have caused havoc among Russian front-line positions, helping Ukrainian forces to halt and even repel Russian advances.
There have been rapid advances in the use of AI and cheap interceptors to help protect Ukrainian cities from the scourge of Russian drones.
Fedorov also conducted a forensic analysis of procedures and practices in the ministry, aimed at reducing bureaucracy and improving efficiency.
Arguably, it was a never-ending task.
"The Ministry of Defence is a swamp," Stupak said. "It's made of very solid material and it's very difficult to establish new technologies because lots of people have been there for decades and they are don't share his vision of digitalisation."
The concern among many observers is that Fedorov's departure will bring his ambitious reform and innovation programme to a screeching halt, despite Zelensky's assurances that nothing will change.
With autumn and winter on the horizon and Russia likely to launch yet another assault on Ukraine's battered energy grid, some fear that the country will be more vulnerable.
"I'm very upset that all this progress, which was built by Fedorov, will be just destroyed and reversed in one of the most critical periods of the war," Daria Kaleniuk, executive director of Ukraine's Anti-Corruption Action Centre, said.
Kaleniuk says the crisis also reflects badly on Ukraine's leader.
"It sends a very bad signal," she said. "President Zelensky doesn't care what the people of Ukraine think, and he is also not accepting inside his team people with legitimacy, subjectivity, who are able to initiate solutions and results. That is very destructive for Ukraine."