He is here because he was arguably the best player in the world last season.
Suarez failing to score at Barca is due to the style of play being so slow and safe. No point buying a player to not play to his strengths at all.
It seemed he was bought to bring another dimension but all that has happened is little has changed and they are trying to fit him into the team regardless.
If the tactics remain the same he will indeed be a waste of 80m but it wont be his fault.
The system has indeed changed to accommodate him. When is the last time we played our usual 4-3-3 with wingers and Messi as a false 9 with a tight knit midfield designed to support them? It's not like we're shoving him on the right wing or just playing Suarez as our sole striker/false 9. The tactics, if you can call them that, that we use now are dramatically different than what they have been in prior seasons and it's actually quite a bit worse. It's not like we're not playing him as a striker and putting him in positions to score, either. His first touch is bizarre and his instincts in front of goal have vanished from the days when he would fire rockets past the keeper using nothing but his own genius. He's not playing any better than Pedro right now, which honestly is about as bad as you can possibly be when it comes to Barca forwards.