I agree with the premise mate. It's not easy to do though is it? To find a lad who's flopped at Inter at 20 who would actually go on to be world class. It's not impossible, but it's very difficult. I think e have tried that, to a degree the signings of Digne, Gomes, Mina, Kean, Iwobi etc all fit this (albeit they are a little older so not so much risk). There's a lot of risk though.
Signing a 27 (will be 28 by next season) Coutinho is ultimately a less risk less reward version of doing this, isn't it? I mean you know what he can do, the question is does the manager believe he can get the best out of him again? I don't think anyone is talking about whacking a big load on him,but either a 1 year loan (or even a complex 2 year loan to take him until the end of his contract) could be really prudent.
In general, everyone tries to do the above. It's hard. We all know the players who are linked, Felix last summer, Havertz, the lad from Lyon etc. It's not easy.
I am for a balanced approached. I have seen us sign a lot of really good players over 30. Barry, Richard Gough, Nigel Martyn etc were all absolutely fantastic here right into their mid (or even late) 30's. A lot comes down to professionalism, but I do think there is a tendency to write off older players a little bit too much.