While Corvus Glaive from the Marvel Cinematic Universe has the most powerful blade in the universe and Ebony Maw can do whatever he wants with his mind, Thanos doesn't have any special power. Doesn't that make them more powerful than Thanos?
Corvus is skilled with his blade, and it's a powerful weapon on its own. But we don't know how, or where he got it, exactly. Who trained him...or who gave it to him to begin with. In the MCU nothing is explained about him beyond whats on screen.
Ebony is also a powerful telekinesis user. You may be correct, he may potentially have the ability to fight against Thanos. But we also saw in the MCU that a teenager was able to kill him with little effort and clever thinking. (Well, with Tony's help.)
Unfortunately one cannot mix the powers and abilities of the comic versions of characters with the MCU version of them. They are inherently different mediums with different sets of rules and movies just don't have the decades of storytelling behind them.
We see what we see.
Thanos is most certainly a powerful character, physically for sure. His powers aren't really shown off, besides he's a strong (physically) purple alien that can hold an infinity stone in his hand without exploding! He may not be as strong physically as the Hulk, though as we saw at the beginning of Infinity War, he had no problem beating the Hulk with skill.
And this is the important part. Thanos is a smart guy, a leader, he has the ability to convince. And mostly certainly does lead a powerful military. For Corvus or Ebony or even Ronan (until he got the power stone...then he seemed confident he could do something) it's not worth it to fight against him, his military will just obliterate you afterwards.
Importantly, he's also what some might call a psychopath...and he definitely attracts other psychopaths towards him. Ebony believes in Thanos' plan for the universe as if it were a religion, for him it probably is, and he wouldn't even dare fight Thanos anyways. Corvus doesn't speak much...it's hard to say what exactly his thinking is. Though, it's probably not that far away either.
Corvus's blades and abilities likely pale in comparison to Thanos' skillset regardless of the glaives sharpness.
Ebony Maw may have the ability to go toe-to-toe with Thanos on a one-on-one. But if Peter Parker can take'm out, Thanos likely can too.
In the end, Thanos' horsemen believe in Thanos like a prophet and wouldn't dare fight him to begin with.