Cena's final year was a bad case of WWE booking, and a farcical joke at best, but booking Gunther to be his final opponent was probably the best decision they could have made.

Why? 

For me he is just an old school wrestler. No super flashy moves, no stupid gimmicks, no idiotic dances or one liners, just get in there and fight. 

For too long WWE has been about theatre and the spectacle, which I guess ties into the entertainment aspect of their business, but I don't see anyone complaining about anything Gunther has done up until this point until he was rumoured to be the final opponent. 

What better way for Cena to go out, than to be brutally demolished by one of the hardest hitting wrestlers to have graced the squared circle since the likes of JBL and Seamus in his prime? 

Have the match go back and forth for half an hour or so, a true slobberknocker to show off Cena's never give up and never give in attitude. But eventually the true final boss of wrestling (not a reference to Dwayne, I just genuinely believe Gunther has that aura) overcomes all Cena's willpower and beats him to a pulp, leaving him in a heap in the ring, standing over him and signalling his dominance to the rest of the locker room by demolishing the GOAT in his final match (leading to his push to a title again).

But the true send off is when Cena gets to his feet, despite the beating he just received, shakes Gunther's hand and then leaves his armbands and wristbands in the centre of the ring and walks up the ramp, showing that even though you get knocked down hard, you can still get back up and keep going.

That is how Cena would want to go out. 

My take: For all the talent WWE had to choose from, this was the best option they could have made.