It’s been quite a long while since I’ve seen the film. So, what if the younger Tom Riddle was successful of coming back to life, wouldn’t he become a dangerous threat to the real Voldemort?
Surely he would be as selfish, evil, scheming, and ambitious. He would attempt to eliminate his frail counterpart in Goblet of Fire, a seemingly loose end.
And why didn’t the other Horcruxes have the same Tom Riddle manifestation?
Who is to say who the “real” Voldemort is? A young, strong, handsome Tom Riddle certainly seems more real than a ghostly bit of soul in Albania.
You forget that this soul fragment had a rudimentary body only because Peter Pettigrew sought it out in Albania. With Voldemort returning to full strength two years earlier, Pettigrew would not seek out that soul fragment on his own, though Voldemort himself might do so.
This is a bit less clear. Some people have speculated that as one of the earliest (first?) horcruxes that Tom made, the diary was imbued with a “larger” piece of soul than subsequent horcruxes.
It’s also important to note that the diary was intended to be used as a weapon to “purge the school of Muggle-borns”, whereas the other Horcruxes were simply safeguards for parts of Tom’s soul, tethering him to life. It certainly seems as though Tom put “more of himself” into the diary, given that it could respond in writing and display memories.
Whether the diary was was intended to just release the Basilisk or was to serve as a “full backup” of 16-year-old Tom Riddle is unclear.