Which I am assuming we have tried obviously last summer. We tried absolute top drawer lewa, muller, bale, ronaldo etc and also players like kane, mane, pogba, benzema etc. At least some of this must have been true, if we go by rumours. LVG plan-A could not have been Rooney as striker with untested Martial/Wilson as back-up, and even if it was the plan it is not Rooney's fault if misplaced confidence was placed in him (specially when we were going to play CL as well). But unfortunately because of various reasons it is not just simply just a matter of putting money on the table. Multiple reasons - we are not the club players aspire to play for over other top clubs, foreign players prefer London, other players are well take care of by their current clubs or not at the end of their contract. PL has lot of money and even clubs like Southampton can easily fend off advances from top clubs, if they are interested (not all the time though). So while I think it's hard to argue against the fact that we should have replaced Rooney (or at least added to the squad) two top players in forwards roles, we couldn't get them.
If Rooney is costing us 13m per year in salary, I am sure that is puny amount for the club and we didn't back out of any potential deals just because of that 13 million. We in fact paid 35 million (which can go up to 57 million based on bonuses) for a young and untested Martial and we would probably have paid much more to any top-drawer player. The point is that the salary is only one factor. Shweinsteiger is getting 200k per week but no one says that he should be playing better than Shneiderlin because he is earning twice. We all take other things into account other things (his age, his transfer price, wages etc.). And mind Shweinsteiger is on a 3 year deal which is only one year less than what we offer even to young players.