unfortunately, most are, if they are designed right.
the best, most all-round rider wins. and after three weeks the difference between that rider and others is more often fairly large (or at least lacking in suspense).
for real suspense, you need at least two riders who are both top five in TT and climbs (and who don't crash)...TDF 89 anyone? But this is rare.
none of Merckx's wins were close (Ocana crashed in 1971), but his defeat in 1975 was a thrilling TDF!
none of Hinault's wins were close, but his defeat in 1986 is the most remembered.
Anquetil's most memorable win was his last with Poulidor close but never really really going to win with the final TT.
none of Indurain's wins were memorable at all (probably the most boring period in TDF history), and yet his defeat was newsworthy.
It is often the eventual losses of the dominant rider of the time that are truly memorable.
One of the reasons I actually think Lemond is so popular is that his wins were almost always as the underdog... the underdog to the patron Hinault in 1986 and the defeat of the blaireau, the comeback in 1989 and the, yes, comeback in 1990 from being really overweight and out of shape and being more than 10+ minutes down on Chiappucci.
To enjoy the TDF one has to enjoy exploits by the dominant rider of that time. You can enjoy a TDF like Merckx's 1969 win or Ocana's 1973 win by the panache demonstrated by the winner -- same can be said, in relative terms, about Pog's win this year).
And, frankly, I would not want it any other way. GTs should always crown the very best all-round rider and not have superficially created drama by lessening the challenges or putting things out of balance (see Giros of the 1980s that catered to climbing-challenged Saronni and Moser or the ridiculous Vuelta where Maertens won 13-14 stages).