Off the bat, the 1 year of prep is ridiculous. No one ever has that long in comics, and it's kind of impossible to speculate with that much time. Realistically, if they went hardcore with prep, they could both, in theory, come into the fight with abstract-busting capability. So it really takes their base powers off the table quite a bit.
How exactly, especially against a similarly prepped Strange?
I don't necessarily disagree. But when people make claims in prep-matches, I sometimes cringe at the lack of justification. You still need to know the means by which he accomplishes the feat.
This, deliberately or unknowingly, is trying to deflect the burden of proof away from you. You're the one who made a positive claim. The burden is upon you.
What has Thanos done that doesn't involve artifact retrieval (banned by the OP) that makes you think he'd casually drain classic Strange? I'm not saying he doesn't have a feat at this level, I'm just saying that you need to provide it before your claim can be taken seriously.
Because I don't care about the outcome here, I just enjoy trying to inspire critical thought and reasonable justification to opinions. You may have both in this situation, but you have yet to provide them.
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He has high intellect and is a master mind. Granted his planning generally involves procuring artifacts of immeasurable power. He still seems like he would do better than Strange imo. Since to my knowledge Strange has done nothing worth mentioning with prep.
Well, let's look at these statements individually.
No objection.
You begin to see my point, I hope. Your first statement, while true, is not an a priori victory for Thanos.
This is an opinion. Granted, it's not an unreasonable opinion. But in light of your original statement that Thanos drains Strange's power and steals it from him, this does not constitute even the beginning of a defense of that statement.
Thus, you can reasonably hold that you think Thanos would do better, but must concede that we lack evidence to justify the utter steal-stomp that you led with.
Again, evidence to support the earlier statement may exist. I don't think it does, personally, not without lopsided prep for Thanos (which this is not). But the point is, no evidence has been produced.
I won't be as cruel as cdtm's smilie, but this does reveal a lack of knowledge about Strange. He possesses many powerful prep feats.
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So, to drive my point home with an example, this is why Reed is so powerful in fights. We tacitly assume prep-domination from many characters, but often times without the proper justification or without an idea of what exactly they would do in prep. Reed's one of the few with numerous Skyfather+ feats of prep that are easily identifiable, whereas "They just do" or some variation thereof does not cut it for most.
Anyway. This is a tough one. These are 2 characters that float all over at the top of the pond. Both have shown power and ability that can place them high in the food chain. They can, pretty much, hang with almost anybody.