you're telling on yourself how little you engage with people of different beliefs. conservatism is a vague, otherizing term used to cover an absurd range of beliefs, including people who are very opposed to classism, poverty, or just about any single idea. it's no more valid a categorization than empty groupings like "left", "West", "East", etc. Like, the Catholic Monarchs were hyperconservative but commenced the legal abolition of slavery by the late 1400s (by the time of their son in law, slavery was legally abolished throughout the Spanish Empire (enforcement took much longer across the Empire, but esp. where the Crown was strongest, slavery was significantly reduced)) while they also conducted la Reconquista and the unification of the pre-Spanish kingdoms.
but another point: Dimitri never took the time to learn ideological leadership or policy design. He treated his studies as chiefly martial and, to a large degree, he never tried to be a person who could institute reform. As real as political limitations are, trying is a low bar. Having an ideology is a low bar. Dimitri is concerned a lot with securing power, but he genuinely does not put in the effort to lead the people in terms of belief, nor does he obtain help from his allies to compensate for his weakness there.