You say we are weaker in other areas than centre back, I somehow do not think Stevenage's players or management would agree with you on that claim.
As for playing the loan players, it's highly unlikely that we will see much of Kell Watts except in emergency, but he has been a little disappointing this season, that probably leaves a straight choice between Morrison and Goode in the matchday squad, Sessegnon is the utility player in the squad who can fit into the full back, central defence or midfield rolls, so essential to cover those areas.
I fully agree with you that there are other areas we need to recruit far more, but we all know the restrictions that are preventing us doing so. I think Maloney's reasoning is strengthen the defence to cut out the 'soft' goals we concede, which are mainly from errors and being out muscled, with that he believes we just have enough to get us a few goals and some points board so we don't have any relegation worries, which was always his brief this season.