Is it really possible to be really good with only one hand?

[Zageron]

Is it really possible to be really good with only one hand?

Sort of. The definition of AAA god and FC god are much different. You will NEVER be an AAA god with one hand. But you will be able to do some sick FCs.

Is playing one-handed an extreme disadvantage or is it just a small thing?

Yes. It's a disadvantage, and we choose to play that way.

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I think I'm the only pure one hander, thats very good, left. But more are welcome. It's getting lonely here.
Edit: Yay arsonists is with me!

Will I have to change my playing technique if I wish to advance any further?

Depends on how you want to progress, and when. It takes multiples of times longer to get good with one hand than it does with any other style. If you want to AAA stuff, change to spread.