When things don't go the way people want, they always cry "PLOT NO JUTSU!" It's like a mantra.
People need to get real.
Obito fought the WHOLE Midrange Division of the Allied Shinobi Forces aboard the Gedo Mazo...
...then fought Bee (plus Gyuki) and Naruto (plus Kurama)...
...then fought with these again plus Kakashi and Guy...
...then got stripped of his best weapon (the undead jinchuuriki)...
...then kept fighting against those (Naruto, Bee, Gyuki, Kurama, Kakashi, Guy) alongside Madara...
...then fought alongside Madara and the Juubi VS THE WHOLE FRIGGIN' ALLIED SHINOBI FORCES minus the Five Kage...
... AND THEN FINALLY had a duel with Kakashi.
Whoever thinks Obito had really a chance of survival is either a Obito zealot worshipper or is clearly in denial. Obito HAD to fall at this point, he is holding his own since more or less chapter 564, which means it took two armies, a number of insanely powerful shinobi and SEVENTY-TWO chapters to bring him down.
Either you want to make Obito look much stronger than he already is, or you're trying to to make Obito look much weaker than he already is; else you honestly got to admit Obito had to lose this fight. A different outcome was kinda absurd, not to mention it'd be a boring read if Obito would still be standing uber alles.