Congress is more in charge of taxes and budgets, not the president. However, it would seem Democrats in general want to use this for the upcoming elections (along with nearly everything they promised last election).
I would personally love more information on this topic. I view elections for Congress to be much more important than presidential elections.
Looking around I found this website via her Wikipedia entry. It's a website that measures how close a member of Congress votes with Biden (but only from 2020 to 2022) and Sinema and Manchin seem to vote with Biden on nearly everything he wanted. My personal opinion is those two senators along with Biden act as the "centrists" (right of center) that we expect them to be.
That's why I added "against things that mattered." They mostly voted along party lines on the small stuff, but for the major things that would have been impactful then one or the other would swap their vote or hold back their vote until the bill was watered down enough. It felt almost like it was planned which one would be the block so that neither was the block too often. And eventually the bill would get watered down enough that it wasn't as impactful and then they could vote yes.
I did get your point, I just wanted more examples. I do believe you, it's just the info I found must have been incomplete or counted the times they voted with Biden once the bill was watered down.
It did lead me to an interesting point. I'm used to seeing independents being progressive. Not leave the Democrats because they are not centrist enough.