I wouldnt even buy Lemar for 90m, so leave that aside.
The main problem I have with your response is that you use that argument about "past young flops we have signed" time and time again whenever people urge us to sign quality young players. Its not relevant who we have signed in the past. You seem to believe all young talented players are considered by everyone as the new Messi when that is far from the case. You have to judge each players individually. Many young players are simply stupid and get hyped up based on physique beyond their age or other attributes.
Did you or did you not want us to sign Ney and Umtiti? Did you want us to sign Lemar when he was a 25m player last summer? Or did you dismiss him using the same argument you use now when he is at 100m? You argue against Goretzka as well. A player who would cost 20m tops. It seems like if the player is young, you simply do not want him. We can always try to chase superstars from rich clubs but we almost never sign them, because its almost impossible in this day and age.
You are using a hindsight.
It is easy to say: we should have bought Dembele for 20 and Lemar for 25.
Again, try this:
Name 10 players TODAY who are available for 10-30 Millions and who seem like a good deal (players like Lemar in 2016 and Dembele in 2016), so even before Dortmund's/Monaco's good last season.
Again, from 10 players in the price range 20-30M, 8 will turn out into nothing special in 2 years, and 2 will turn into Lemars.
The million dollar question is: how to pick one out of 5 or 10 which will turn into a Lemar?
Because, if you buy all 10 players for let's say 30 Millions, you will spend 300M and get 2 Lemars in 2 years, whom you could have bought for 100-120M later, without a risk (and without waiting until they develop slowly).
If you get my point?
Buying youngsters is good ONLY if you hit a jackpot with a youngster whom you buy for 30M and who turns into a 100M player.
If you buy 5 youngsters for 30M who all flop, you haven't done anything and you could have bought proven Coutinho/Griezz for that money.
So, yes, if you/the board can pick 2-3 youngsters for 20-30M who will turn into new Lemars in 2 years: do it, I am with you.
But again, maths, statistics, logic and history will tell you that for every youngster, chances are 1/5 or 1/4 that he will make it here.
And at the end of a day, statistically you will get this:
1) buying 5 youngsters for 25M each. Total 125M.
4 of them will flop and turn into 10M players and one will turn into Lemar (BUT, you will have to wait for him for 2 years).
In total: you invested 125M, you will get one player worth 125 (one out of these 5), and you will return 10+10+10+10 from sales of these 4 who flopped.
But, but you will lose 2 years without trophies while trying to find out which one of these 5 will make it here.
So, 2 trophyless seasons, one Lemar in your team and 40M earned, let's say.
Basically, you have spent 125 Millions to get ONLY one Lemar after 2 years of waiting and developing.
2) scenario 2: you don't buy any youngsters, you buy Coutinho/Griezz RIGHT AWAY and have him for 5 years.
You will win trophies right away, you will get a player whom you wanted.
You won't get re-sale money back and you can't have him for shiny "10 years".
But you will win more trophies both right away and probably long term.
With youngsters, there is always that shiny: what if, what if (a chance to get 2-3-5 players for cheap and to have a player for 10 years).
With Griezz and Cou, you get what you see, you pay a lot, but you get the immidiate impact.