The Dutch coach first arrived in the Kingdom as assistant to Bert van Marwijk during Saudi Arabia's successful qualification campaign for the 2018 FIFA World Cup before returning years later as a head coach with Al-Hazem, Abha and Al-Adalah.
Having experienced the Saudi Pro League both before and after its unprecedented investment in global stars, Coumans believes the competition has become one of football's biggest success stories. But he also believes the league must be careful not to lose sight of its long-term objective.
Speaking exclusively to Football Presse, Coumans praised the rapid growth of Saudi football while warning that opportunities for home-grown players cannot become an afterthought.
"I was in Saudi Arabia for the first time with the national team," he said. "Honestly, that was the best time.
"We qualified for the World Cup in Russia and with this team we really made a huge step in improving the way of playing and improving the qualities of the players.
"There was not really a belief that they could make it to the World Cup.
"So it was a huge achievement."
Coumans still recalls the emotion of the decisive victory over Japan in Jeddah that sealed qualification.
"Winning that last match against Japan 1-0 was one of the most emotional matches I had in my career. The stadium was full, it was very hot and the atmosphere was incredible."
Returning to Saudi Arabia several years later, he found a league transformed. Global names had arrived. Investment had accelerated. The quality on the pitch had risen dramatically.
"The last three years I was at Al-Hazem, Abha and Al-Adalah as head coach.
"It was also a very good experience for me.
"You see the league is developing a lot.
"A lot of foreigners are coming."
Cristiano Ronaldo's arrival at Al Nassr proved to be the catalyst for that transformation, opening the door for dozens of elite players and coaches to follow. The league has since attracted some of Europe's biggest names and continues to grow in profile after Al Nassr finally secured the Saudi Pro League title with Ronaldo leading the way.
Coumans believes there is no question the influx of international talent has raised standards across the competition. But he also sees a challenge that Saudi football will have to address in the coming years.
"The only negative point about bringing a lot of foreigners is that your local players will not have that many chances to get into the first team. So they will play fewer quality matches because most positions are taken by foreign players.
"So in a way, yes, it's good for the league. Is it good for all the local players?
"I doubt it. I think there could be a better mix."
It is not, however, a completely one-sided debate. Working alongside international footballers has also helped improve professionalism throughout Saudi clubs.
Coumans believes local players are benefiting every day simply by sharing dressing rooms with world-class professionals.
"You can also see it differently because the local players train with better players on the field. So they can learn more.
"They become more professional.
"They learn how to live better, how to work better and how to play better."
The challenge, he says, is finding enough time for that development to happen naturally.
"Unfortunately, the big teams play so many matches that your training time on the field is reduced a lot. So we'll see in the future what it will bring."
As for Ronaldo himself, Coumans believes the Portuguese icon has entered a defining period of his Saudi career.
After years of helping transform the league's global profile, the expectation has shifted towards sustained success on the pitch.
"I believe Ronaldo had a lot of influence on the squad. So it's more his responsibility to win the title."
Coumans was proven right as Al Nassr ended their wait for the league championship, with Ronaldo playing a decisive role throughout the campaign.
Looking ahead, he expects the battle for domestic honours to remain fiercely competitive despite Al Nassr's breakthrough.
"There are four top teams.
"Al Hilal, Al Ittihad, Al Ahli and Al Nassr. They are on a different level than the other teams.
"So it will be very competitive and we will see what happens."
Having coached both internationally and domestically in Saudi Arabia, Coumans believes the country's football project has already exceeded many expectations.
Yet he insists its greatest success will not ultimately be measured by the number of famous names it attracts.
Instead, it will depend on whether the next generation of Saudi footballers can emerge stronger from playing alongside them.
For Coumans, that balance between global ambition and local development will determine whether the Saudi Pro League's remarkable rise becomes a lasting legacy or simply a golden era built on imported talent.