IIRC (it was, as I said, a while ago), I basically looked over a list of the most expensive transfers in football and calculated whether or not that player turned out to be a success. This one, iirc -
https://en.wikipedia.org/wiki/List_of_most_expensive_association_football_transfers
From a brief examination, most of the players on that list were individual successes for their clubs - the few failures like Benteke and Veron were the ones I factored into the '1 in 3' assertion, and I had to mark a lot of players that I was ambivalent about or didn't know enough of as 'failures' to even reach that figure. Still, I figured that made an *extremely* unscientific examination a bit more rigorous.
There's no doubt that a good scouting process aids in finding the right players, but it's harder to quantify - an objectively 'good' scouting system is hard to accurately describe, and varies with the times. Hence, the assertion, which is based on a bit of common sense, really - if a rich or successful team likes a player enough to get him into that list of most expensive players of all time, there's a good chance that a) he has qualities similar to those of the rich/successful club's already existing, talented players, and b) that the club's commensurately expensive and no doubt well-supplied scouting network will have marked him as one worth paying for.
As for us being able to afford big signings, we probably could, we just choose not to. In an environment where Crystal Palace can afford to offer 30 million pounds for Christian Benteke, Spurs not being able to afford a similar commitment is something hard to believe. We want to spend the TV money on the stadium, and we want to keep the balance sheets looking good - while my populist 'the owners aren't spending anything but the fans' own money' views still stand, there's nothing innately wrong with prioritising those things over spending in the market. But we are doing that, no doubt about it.
And as for N'Koudou, like I said, it's just a confusing signing given that N'Jie had an extremely similar profile when he was signed last year, and I thought the new mantra was to give signings like him time instead of shipping them off. Plus, if we did consider him worth replacing, it is a bit strange that we go for someone exactly like him, with a similar profile and from the same league for much the same price - creates the question of whether we want to upgrade on him or if we just want another N'Jie-type player around for a while.
Either way, the transfer is just something to be confused by, as far as I'm concerned. If it had been in a problem position, then it would have been a concern - but we're stacked in attacking midfield, and trading N'Jie for N'Koudou, or adding N'Koudou to the side as a whole, isn't overly disruptive or distracting from key areas. That's a luxury we now have thanks to the primary areas of concern being addressed by Wanyama and (after a frustrating delay
) Janssen.