Concede what exactly?
I have acknowledged that he could have developed faster/quick/better. But NO ONE knows of this to be true, because it didn't happen. It's therefore speculation. The claims that he wasted the last 'x' years at Spurs because he didn't go out on loan is based on speculation, because he didn't go out on loan.
If he's playing shit at Southampton then is the time to pipe up a lay claim that's because he wasn't loaned out sooner. But if he's playing well now then there is no need to speculate anything, on the contrary just praise and enjoy the fact that having spent 'x' years at Hotspur Way he's now playing well on loan.