Thanos is powerful no doubt...but there are lots that can beat him and despite earlier comments, Doom could...lets be honest he took over the multiverse and ripped Thanos skeleton out...so yes Doom can beat him in strategy if necessary but have rarely had the chance
And Thanos became the Marvel Universe. He didnt just take over the multiverse. He became Marvel. TOAA.
His obtaining the heart of the universe was the greatest level of power in Marvel.
Nope. Thanos' is Marvel's greatest schemer. It's part of the character.
Intellect/scheming>Durability>Power.
Doom already had the Beyonder's powers when Thanos got involved.
Marvel's The End, which you are conveniently disregarding had Thanos and Doom both prepping and strategizing against the same character. Thanos came out on top.
Your hypotheticals are baseless because this has happened IN CANON (before it was erased). They both had a strategy, and Doom failed while Thanos succeeded on a grander scale.
If Thanos has no prep, fine, Doom can prep against him. But you give them time to both strategize against each other, Thanos will out smart him and out plan him. This is an indisputable fact, it happened in canon.
Doom ripped out Thanos' spine in a cheap money grabbing retelling of Secret Wars...in which Doom was already God Emperor Doom and omnipotent when Thanos got involved.
In The End, the prepped simultaneously, both creating their own plan with the same goal...the only time they were on even footing. Thanos succeeded, Doom failed. That's it.