with Sinema and Manchin seemingly on board
Neither has committed to the reconciliation package, only that they want to see details. Fair enough. The question is if the current bi-partisan package passes (which is still uncertain), and conservative Dems like Manchin and Sinema get their roads & bridges, will they go on to support the larger reconciliation package?

It will be interesting to see how the financing of both/either shakes out. Republicans are steadfastly against raising corporate taxes (of course).

you are probably well aware, part of the normal give-and-take haggling and deal-making engaged in by legislatures throughout human history
Of course I am. But the weak-sauce comes in because Democrats almost always cave to the GOP so easily without much of a fight, and legislation ends up being much closer to what the Republicans want than what the Democrats want, more often than not...