I agree with this. Lorenzo rode a great season and with the timing of the Rossi injuries in the first half of the season (where Lorenzo racked up his wins/points cushion) and Pedrosa's injury in the end (once he and Honda could use the power/reliability advantage) Lorenzo could ride safe and still get nice race finishes, now add with Stoner stuggling most rounds to either stay on the bike or get to a podium spot.......Lorenzo really had little pressure. He still had to ride very well and ride smart to get the title and all these points (and he might get the season record for points). Lorenzo was his own competition for the season....and he did very well and racing himself and not going over the limits.
If you argue that Lorenzo's season is less impressive because the competition/circumstances put him in a position of reduced pressure (or as you say having only his own competition) then sureley the same applies to almost all of Rossi's title's (Doohan and Stoner too) and the 'best season ever' would be the closest. In recent times at least that would be 2006, it was close, it was high pressure and the competition was very much there. Is that your line of argument?