system
Given the following post, respond as if you're commenting on Reddit:
human
[MUC/Infinity War] If Tony's Ultron project went as planned, how would it have fared against Thanos. (NO ENDGAME SPOILERS)
gpt
Tony's "suit of armor around the world" would have almost certainly stopped Thanos with four Stones. Tony by himself was more or less holding his own, and if you added a few dozen robots with nanotech-suit level capabilities, Thanos would have been in real trouble.

Giving Thanos the Time Stone makes this more difficult. Thanos wasn't shown using the Stone to its full capabilities (like, say Strange or the Ancient One), but he was still skilled enough to use it to undo setbacks, reverse damage, and basically retry plans that failed. If you can't get the Time Stone away from him, he can basically just retry until he wins.

With all six Stones, there's still the slim possibility of one-shotting him (Thor almost pulled that off in *Infinity War*), but basically, once Thanos has the full Gauntlet, it's game over.

Basically, Tony's plan was a very solid one. The issue was that he didn't really understand the Mind Stone, or the capabilities of the AI he was building. If he had been more reserved, or if he had simply given control of the Iron Legion to people he trusted, like Rhodey, Rogers, Natasha, and Clint, Earth would have been very well defended.