You think it's too simplistic because what you've laid out there is your perception not the actual thoughts of those in charge. They were examples of players who would have been more than willing to fight for a place on a great contract (Mendy was playing in Ligue 2) and it being a world cup year wouldn't gave deterred either imo. I can think of another too, look up Junior Firpo from Real Betis.
As I said in the post as well, Mendy was less than 5m and those are just three names off the top of my head which would be worth the investment and I'm a layman who doesn't have a worldwide scouting network.
Finally you say the season was over in January? Are you one of the people who don't want European competition next year? Because that's a leg up in attracting better players in the summer and regular midweek games is something our squad should get used to year after year.