I don't completely agree with you because the performance of Lukaku is this season is not good enough to say he worth trying hard and paying a huge amount of money for him, Lukaku was injured in many games and he couldn't help his team for weeks, however after getting recovered Lukaku could show in the last week but all we saw from Lukaku was just in a few last weeks which is not enough to say he had a good performance.
It is true that Lukaku is a risky transfer and even though his statistics are alright, it is as you said. Injuries are a problem but also instability in his performances. But the transfer fees are at new heights anyway. When €40 million was record breaking a decade or 15 years ago, it is almost nothing these days. Usually I would agree and say that it is an expensive transfer given how much money Chelsea wants and how Lukaku did perform last season or was injured, but what if those sums are the new normal? Is €40 million still too much?
The risk can even go far when we know Lukaku is getting older and after getting older he will get injured more often and he will need more time to get recovered, while they pay too much money for hiring him but I think Lukaku doesn't worth this huge amount of money.
Inter Milan needs a player like Lukaku but still, they can find younger and better options instead of sticking to Lukaku.
Age is always a risk but at least it is a risk that is known to a certain degree. Nobody would expect a player who gets older and older to become healthier, not at least in the 30s. But that is why Inter is hesitating for a good reason. The amount demanded by Chelsea isn't reflecting the true value of Lukaku, but as I said before, what even is the true value of all these players? Is Neymar worth 222 million? Or Mbappe, is he worth 250 million? That is why on the other hand I think it doesn't even matter whether Lukaku costs 35 million or 40 million.