I agree with Manchin on this point

In this clip Manchin asks Merkley about the proposed rule change to the filibuster. He wonders if it's possible to enter into a talking filibuster now without a rules change. And that's exactly what Rule 19 allows for. However Rule 19 also allows for Amendments and points of Order, whereas the change to the filibuster rule would not allow for any of that. The latter is what Manchin opposes. 

If the Senate had not moved for Cloture (Rule 22) and instead just continued to keep the debate open under Rule 19, then Manchin is right that in effect that would itself be a talking filibuster. The Senate could have kept up that debate, along with all the Republican proposed Amendments and objections, which would indeed have taken several weeks. But it would also extend that debate to be covered in the media for an prolonged period and allowed we the people to become much more aware of the voting rights issue. And the result at the end of all of the Republican's obstruction, when they finally wore out due to exhaustion and public outrage, would then be under Rule 19 a simple majority vote. There would then be enormous pressure on Manchin and Sinema to vote for it since they claimed to support the Bill but not the rule change.

So why did the Democrats shoot themselves in the foot by doing it this way, knowing it would be defeated by those two in their own Party? Were they too lazy for the prolonged fight it would have taken under Rule 19? Perhaps Wallner was right after all when he laid out exactly how the Dems could have won this fight under Rule 19:

"They want legislating to be easy, convenient. The president referred in his remarks to the election officials and voters who do 'the hard work of democracy.' [...] Senators must be willing to do 'the hard work of democracy' if they want to make democratic self-government work." 

They took the easy way out instead and the result is that there will be no federal curb on the fascist State laws destroying our right to vote and democracy along with it. Self-righteously accepting defeat under these conditions is tantamount to complicity. Which is exactly why many of us progressives are sick and tired of their loser bullshit.