If we are talking only about the Bakumatsu and the Boshin War, then it is a complete mistake to think the revolutionaries were fighting to Westernize Japan while those on the side of the Tokugawa were fighting to preserve Japanese culture. Is this a common misconception? I've only ever read the actual history, not any of its western depictions.

If anything, the revolutionaries had much stronger ties to the jōi movement wishing to expel foreigners, as in they were pretty much the same people. Meanwhile, it was the Bakufu leaders who were working hard at trying to open up Japan though in as palpable a way to the Japanese as possible, though out of the realities of the situation more than anything. For all its troubles, the Bakufu received the ire of the jōi movement. They labelled the Bakufu as weak and unable to protect Japan, soil the sacred country with the presence of foreigners, and as traitors for agreeing to western demands against the wishes of the Emperor and for importing French expertise to modernize its military. They made the Bakufu's task impossible by attacking and killing foreigners and Bakufu leaders, and they ended up actively fighting against the Bakufu. Its important to realize here that "Bakufu conservatives" were "conservatives" in the sense that they want to preserve the Bakufu's power, through the opening of Japan and importing of Western know-how if necessary, while at the very least the "revolutionaries" started out as wanting to overthrow the Bakufu to keep Japan shut.

However, it's important to note that the situation was far more complicated, both sides were splintered into multiple factions, and ideas changed quickly. Clans like Satsuma, Tosa, and Echizen were once allied with reformist elements in the Bakufu in politics. These clan leaders were much more in favour of political reform and opening of Japan, and wanted a peaceful jōi through self-strengthening. Meanwhile Mito Domain leader Tokugawa Nariaki was firmly against opening of Japan, saying if westerners want to trade then it should be Japan who dispatch trade missions and westerners don't get to come into Japan. There's also a hierarchical divide, with lower samurai from the aforementioned clan far more likely to support violent expulsion of westerners, and the destruction of the Bakufu that stood in the way of such expulsion, while the clan leaders were much more likely to prefer peaceful reform, or even the opening of Japan as the wish of Shimazu Nariakira the daimyō of Satsuma. The Emperor's court in Kyōto was generally anti-western, but was very divided in whether it supported the Bakufu or the revolutionaries. In fact Emperor Kōmei, despite his personal anti-foreign bias, much more preferred the Bakufu and the Aizu and Kuwana clans who tried to keep the peace, than the revolutionaries who fired cannon on his palace and burned down a large part of his city.

In the end, the Boshin War was not about cultural preservation and whether or not to open Japan. That has already been settled by military failure against the west, and both sides (the leaders anyway) were clear Japan needed to open and both sides were in the process of frantically adopting western arms and military structure. What the Boshin War was (politically) over was that after a period of weakness that caused by quick successions and succession crisis and the coming of the west at the same time, weakness which allowed clans to win some reforms and concessions, the Bakufu (actually ex-Bakufu by the beginning of the Boshin War, as the Bakufu had voluntarily ceded its powers to the Emperor a couple months before) was well on the path to restrengthen and reassert its authority. Chōshu was afraid of getting destroyed for open disobedience, while Satsuma did not want to lose its new-found political influence, which it was about to lose. And the revolutionaries on the ground had long-standing grudges against staunch Bakufu supporters Aizu and Kuwana for so effectively keeping the peace, winning the court's trust, and hunting them down in the streets of Kyōto for all those years.