Counterpoint: Here in Germany there is relatively little centralization. For example, the government could not implement country wide corona measures, which in the end meant that much less was accomplished compared to centralized countries such as France. In France, one can just close borders and announce curfews. In Germany, such measures always end up as the minimum consensus between 16 states.
Frequently, federal politicians pursue policies beneficial for their home state. For example, the current government is dominated by Bavarian politicians, who channel funds and attention toward a state that is already doing well. Indeed this is likely to continue with the next chancellor being likely a right wing Bavarian.
By contrast, people from other states, especially ones with higher population like NRW, feel like they have little to none representation in a federal level. This gives an incentive to vote for opportunistic demagogues.
The same thing is probably happening on an EU level, where many people feel their local government has less power than before, but the EU institutions are dominated by countries with different interests. For someone from a relative minority, decentralization seems to be a one way street. If some countries do their own thing, then I would like my country to be separate entirely.
So I‘d say decentralization can also endanger democracy, as only complete separation can really be fair. In a centralized system, however, there is at least the chance that the central governance actually represents all of the population.