He was playing for a small team, but having quality player like him, coupled with few other decent ones, made them competetive for that era of their club. They had less money then others, and earned less then others, but competed because they simply procuded good players from their academy, and had quality coach etc.
There was a difference from now and then, but it was still a status quo and then the others. Even if the gap wasnt as big as now, because back then, you could competently build good teams without being super rich (basic foundations like good football academy and scouting went far), and not everyone buying out everyone when they hit it big, because the sport was less global, and players were contend enough to stay home, for some time atleast, not as frequent or frenzied transfer activity back then (hence a poor provincial team like Ajax ruled Europe then just by fielding youth products that were born and grew up around the stadio).
But still, the rich rich teams like us back then, tried everything to get Riva, with all the alluring promises, but he flatly refused and stayed with his small isle team.