Not necessarily. PIS is a very powerful tool. Using the Time gem allows instant time travel, correct? So theoretically he has two very good options.
Option A: repeatedly revisit his own past at a specific time period like say, after he takes the Gardeners Time gem. Do this continuously, only each time he returns to the normal timeline he brings his past "self" with him. It wouldn't take long, especially with the time gem, before there was an army of Thanosi each with their own Soul, Power, and Time gem, that once existed within seconds of each other in the same timeline.
Option B: not as exotic but still effective, again using the Time gem, only this time he travels to the future when he has the HOTU, telling himself that this victory will finally win him the love of Mistress Death would be more than enough to help him recruit his future self to handle the Anti-Monitor.
At the high of his power the Spectre had to appear to stop him, and even he failed. AM was a Multiversal thread and should be over the Gems of a single Universe. I think the HOTU would be a better challange IF it's not just an Universal artefact .
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So a hodgepodge of hero's and villains varying in power from moderate to high was just barely enough to beat the AM, but an individual that is already insanely powerful and durable, with access to all of the power the does, has, or ever will exist, not to mention the fact that he has accress to other artifacts that give him complete control of either Reality, or Time isn't quite up top the task? That must be some damn fine Kool-Aide you folks have been drinking.
Do you know what ACTUALLY beat the AM? Honestly? Much Much less than Thanos with the IG. Yet, Thanos with the IG can't beat the AM... hmm makes sense to me. Seriously though, you aren't understanding one thing.. First, as stated on panel and through feats.. the IG is AT LEAST Multi-universal, at the least. Second, even if you want to consider it just universal... it makes one God of THAT universe. So even if you believe the AM is multiversal and could do whatever he wants to other universes... as soon as he comes to THE universe Thanos has dominion over... he gets wrecked.
I know. I stated those are all the gems he would need. We were having a seperate discussion because he thinks the AM could even beat thanos with the full IG