Somebody like Yokuslu with the experience to know where to go to receive a pass to help out defenders under pressure, and cover opponents runs, cuts down the number of attacking options for the opponent. Add to this the ability to carry or pass, or hoof the ball, and to make the right decision more often than not to get us back up the pitch, and give attackers a better chance, all improves the team defence. Defending is a team effort, as is attacking. We are weak in the spine of the team and so far have just about managed to get by at this level, Ok we could welcome better players in most positions and CF CH may be a priority along with a goalkeeper, but Centre Mid has been a priority for a number of seasons, and Yokuslu despite age concerns for the longer term, is one of the best options we have tried and might possibly be available to us.
Back on topic: SJ is not doing too badly with his efforts as a sweeper keeper, but is still prone to the same slight misjudgements of bounce, pace and positioning and lack of confident ball handling that has dogged his career with us. Certainly with top central defenders in front of him these would be less catastrophic and he could learn to be a very good keeper.
Unfortunately we will have to develop these defenders because we cannot afford to buy them. SJ does not help his defence to improve, and our present defence does little for SJ's improvement. Catch 22, but with a couple more like Dara O'Shea coming through, and a good experienced keeper to give them confidence we might just get there over time. This of course does not take into account any management and coaching team inputs, which will no doubt be significant.