If we had the opportunity to sign last seasons Diego Costa -fitness issues and the assumption he won't be fully committed saving himself for Atletico aside- for a 6-month period then it would be a fantastic acquisition but it merely papers over cracks.
We'll have built are team around Costa as the focal point, then 6 months later we're left back at square one. The difficulty signing a top centre forward now will only increase in January and given the team would have built to Costa's strengths we'd be looking to plug a very specific hole. Admittedly Costa seems to fit mould as 'targetman' but we'd have spent the best period of the loan figuring out his traits, and playing to his strengths, so it would be a mini-overhaul come January. Face value this seems like a no-brainer, but factoring in everything it doesn't make a lot of sense.
If its Costa for a full season then yes, if its Costa alongside a permanent signing then thats best of both worlds, if its Costa for 6-months then we've really missed the boat in recruiting a replacement for Rom. Costa will surely bang them in for us but (keeping with the boat analogies) we'll be rudderless come January and his goals will only exaggerate the problem we face.