AVB is on record about not being allowed certain players he wanted, and Pochettino likewise was widely quoted about Levy not being prepared to take the next step when we needed to bring in top players.
As to giving the manager the veto, that is totally different to agreeing to buy the players they particularly want. Neither is the argument about whether Levy always refuses to shell out, but about those occasions when he has blocked the manager from getting their choice.
Souness was arguing that one reason we only have a single League cup in 20 years under Levy is because until now DL has always baulked at backing his manager 100%. He is sayimg that now, at last, Conte has persuaded him to agree to bringing in HIS choice of players and that this is what could well make all the difference between winning trophies always falling short at the last hurdle.
Of course we will all have to wait and see on that one, but few will disagree that if Conte IS to be successful it will surely be at least in part because he was able to bring in the players of his choice.