I am, of course, not saying that Twitter is the only kind of public debate, or that public debate did not exist before Twitter.
I am saying that for millions of people Twitter is a unique way to join public debate. Personally, I have interacted with several public individuals who I couldn't conceive of contacting any other way. This is an example of two politics professors taking the time to explain something apparently well known in their circle to me:
https://twitter.com/Jimmytidey/status/757494127537905664
Where else would that happen?
If it does not suit you, fair enough. I find newspapers disinteresting, but I would prefer to live in a society that has them to one that does not. I would also prefer, as with Twitter, that their ownership structure was a little different (I'm in the UK).
I agree that Twitter has design flaws as a medium for public discussion, and I also believe that some of them could be alleviated if Twitter was run was by people with different incentives.
I myself am very happy with the character count, the truth is that the limiting factor is not how long a message you are permitted to write, but how long a message others will be inclined to read. I suspect Twitter is just being honest with us in this regard.
Certainly it is not the place to articulate a nuanced view. It is a place where you can find a unique audience.