Is Bitcoin centralized by mining pools? Before going to my question, I want to make sure the difference between a full node and a miner. Below definition might be too simple, but it is enough to ask my question.


A full node is to store Blockchain and validate transactions.
There are 10000+ nodes running in Bitcoin network.
A miner is to create a next block.
There are 15+ mining pools create blocks.


Then, here is my question.
UASF is an approach by full nodes to enforce miners(pools?) to trigger the activation of soft forks.
However, if a majority of miners agrees on the activation of soft forks, could they activate it? If so, does it mean that only 15 mining pools could control Bitcoin?
However, if a majority of miners agrees on the activation of soft forks, could they activate it? If so, does it mean that only 15 mining pools could control Bitcoin?


No. Soft forks requires full nodes and users to validate the new consensus rules. Miners can "force" soft forks, but that actually wouldn't do anything if no one uses or follows the soft fork rules. Since soft forks must remain backwards compatible, there is nothing that can really be done in a soft fork that would result in miners being able to steal coins or control what anyone else on the network does. Such forks would be hard forks.

Full nodes are what enforce the consensus rules, and users are the ones who run full nodes and create transactions. If no one is running a full node that enforces the soft forked rules and no one uses the soft forked rules, then it's like the soft forked never happened. Miners can't force people to follow the soft forked rules.