True - which is why I don't look at it as "polling right now shows Candidate X does best in these states, therefore we should all fall in line behind Candidate X." Our actions, the candidates actions, news developments - all sorts of influences will change polling and ultimately affect the final vote. There's just not enough signal in polling during primaries to serve as a reliable guideline, because it is overwhelmed by the unpredictable.
Go back to February 2016... who had Hillary losing Michigan, Pennsylvania, Wisconsin to Trump? Nobody. So why should I decide whom to back in February 2020 based on what polling says about any given candidate vs. Trump today (whether nationally or in the states that proved decisive last time)?
What we know is that all the dirty tricks we saw last time will return in some form or other, and how we deal with them will determine the outcome. We have lots of great options for the nomination, what's going to matter in the end is probably less what name winds up atop the ticket than how that person, and their supporters, fight through the general election season. All will be subject to election interference solicited and encouraged by Trump and an endless barrage of lies relayed by media bowing to baseless claims of liberal bias. We will all necessarily have different ideas regarding who will best inspire voters, who will stand up to the rigors of constant attack, and who will make the best president, but I do think those are the right criteria to be employing in the primary season, and polling doesn't tell me much about any of that.