to me the number of side quests isnt as important as the quality of the side quests. the best example of side quests done right is The Witcher 3, deep and interesting side quests, with memorable characters and back ground stories. sure, some are great, some arent as. but thats how things go.
a side quests should be interesting. doesnt have to be long. for example the stranger side quests in Red Dead Redemption. there werent many, but they were interesting, some really interesting. and they made the world feel alive.
Farcry Primal as a SHIT TON of side quests, but they all lack depth and context. do this, do that and its done. and even though im a huge farcry fan, the side quests in primal got boring after a while, despite the gameplay being really solid.
in short, its not just about quantity, its about quality.