Joe Manchin is full of ****.
Him protecting the filibuster is not about protecting bipartisanship. First off, for better or worse, The Democratic Party has always been more committed to bipartisanship than the GOP. The Democratic Coalition is much more ideologically diverse than the GOP. Whatever plans come out of the Dem side, progressives, liberals, and centrist have to compromise on it. The filibuster just gives centrist a disportionate amount of power. Bipartisanship across parties only works when there is ideological overlap, the GOP is too far right and not good actors. So there is not reason for any Democrat to worry about protecting their veto power.
This is about protecting Joe Manchin, and other true centrist's power. If they drop the filibuster, sure the first couple bills that will pass will be dictated by the centrist. They are the marginal vote, so they get the final say. However soon the Dems will make DC a state, and two mainstream liberal or liberal progressives will be in the Senate. The 2022 map looks good for the Dems too and if they can whip up enough energy, and expand voting access, they could have solid turnout they might pick up a couple seats as well. This all pushes the marginal vote out of centrist like Manchin and Jones hands, and into the hands of a mainstream liberal. In other words, the Dems would not need to consider the wishes of Manchin anymore when trying to pass policy. The views of the median Dem and the marginal Dem would be much closer, so Joe won't have the power to slow them down.,and to form those asinine problem solver caucuses that frame everything as "both sides".