Yeah, you look at Lingard and he'll probably want, say, 6 mil a year over 3 years plus a big signing on fee, let's say that's 20mil over 3 years.
Or you sign someone like Lewis-Potter for initial 16m, pay him 3 mil a year, that's 25mil cost over the same period, maybe a little more in add ons if it goes well, but that would be a good thing.
But the difference is that Lingard you can never recoup a penny because at 30+ on high wages there's little to no sell on value, whereas KLP you have a player with a 16m value which you could in the future recoup some or all of, or make a significant profit on. It's like the difference between renting and owning a home.
Maybe you make the argument in favour of Lingard if he's a much better player (is he?) but economically there's no argument for signing him rather than a KLP type.