Yes, there needs to be a tournament to decide who is the best. In any other sport it is determined by a tournament, why should WWE be any different? It could be decided by statistics but and that may show on paper who should be the best but when it comes down to getting in the ring and proving it the results may be different.
The participants in the tournament should be determined by who has won the most bouts leading up to the tournament. Injuries suffered by any one participant cannot be taken into account as a justification not to hold the tournament. It is unfortunate, but the next healthy most-winning fighter should be able to compete.
I am not sure why a title wouldn't be awarded by tournament. By single challenger? It would be harder to keep the interest of the people if the Heavyweight Title could be sought on just any day of the year by anyone challenging. We group things in seasons so we can train, and also so people are interested and go and pay to watch so that Heavyweight fighters don't also have to work at Starbucks. Tournaments are notoriously fun for spectators, and they harbour a healthy amount of the competitive spirit, that has a generally positive ebb and flow. The energy builds, the fighters fight, the crowd is satisfied, they buy t-shirts, to say they were there, and they go home. What could be better?
Throughout the years of the WWE's existence we have seen many people hold the Heavyweight title and many others that could very well have been contenders for the title. A tournament would not only be entertaining to watch but also give multiple contestants the opportunity to prove their worth and have a shot at earning the belt; not to mention a higher chance of seeing your favorite wrestler get a chance to participate.