I wouldn't call it neutral. It still has a development team made up of people who decide the direction of the technology. You don't like a decision and use a fork - now you're isolated from everyone else who is still transacting on the main chain.
The validation of transactions is a red herring in these discussions - the real question of decentralisation is who is responsible for making decisions about the future of the tech and what happens when people disagree. In that respect Bitcoin is neither decentralised nor neutral. Same as Ethereum.
The development team doesn't have the power to decide the future direction. If they release a highly controversial change, no one is obligated to use their code. They could continue using an old version, or switch to an alternative node implementation led by different developers.
Every change to the network is a complex dance between the power of the developers, the miners, the exchanges and services, and the actual coin holders. If any significant segment of these forces don't agree with the direction, then the default is to change nothing and maintain the status quo.
This is what makes it neutral. No major changes to the network can happen without supermajority support among all players, otherwise you risk severely fracturing the network, which is bad for everyone.
Unlike the development teams at a software company, though, the development teams here do not have any special privileges over the software. They only have "control" for as long as their users continue choosing their forks.
If a second "development team" sprung up and had more user support than the existing team, there is literally no advantage the current team has to control the software.
And if a second government sprung up with more support, the old one would be out of luck, too.
I don't think we can simply discount the power these developers wield. They have a lot of explicit and implicit (as in "just install the latest version") trust. Sure, they could loose it, but they can do a lot of damage before doing so.
With software you need to consent to perform each update (I don't think bitcoin core has auto-update yet). This is nowhere comparable to a government in power, which has enormous power and can't be easily deposed. Even recall elections take some time, and can theoretically be interfered by government controlled security forces.
"I wouldn't call it neutral. It still has a development team made up of people who decide the direction of the technology."
The development team has no such power. They can raise a BIP (Bitcoin Improvement Proposal), which goes through rigorous cycles of analysis. A huge amount of paranoid eyes will obsess over any change proposed.
As for the development team itself, there's no THE development team. Rather, it's a highly diverse set of crypto businesses, non-profits, and individual volunteers. This diversity too helps to preserve common interests, rather than specific ones.
Should the BIP survive the first round of extreme scrutiny, next a whopping 95% of miners need to signal that they support the change. But not even that is enough, nodes (validators, of which there are an extreme amount) can still reject the change. Which is what happened in 2017, when miners wanted to increase block size (which reduces decentralization) and the community blocked it, despite a 95% miner approval.
Surely there's no such thing as 100% decentralization or neutrality at a theoretical level, but this is as close as it gets.
Good luck getting any change into Bitcoin that isn't good for every participant of the network. The last time people tried this, users, not even those users with the most Bitcoin at stake, were able to produce enough chaos and generate enough risk that they failed. Ethereum is capable of full consensus mechanism changes that hurt subsets of the network who don't hold the majority of Eth, the latest of which just further entrenched that ability.
I personally prefer the former for that reason, but by your critique, Ethereum is practically conducive to keeping the people who control the protocol small. Bitcoin is probably headed to a version freeze this decade, which is great.
Right now blockchains are essentially being incubated by centralized authorities as they mature.
Eventually, we'll see the ideas behind Decentralized Autonomous Organizations (DAOs) mature and become a viable alternative to centralized authority.
I think that's the plan at least with Ethereum. However, Ethereum 2.0 is still being deployed and what I'm talking about is probably more like 4.0 or beyond.
However, right now there is just no mature alternative. Someone has to own the keys.
Edit: Also, what others have said regarding being able to choose your development team. That's one of the cool things about crypto. Blockchains can be forked with enough support.
The validation of transactions is a red herring in these discussions - the real question of decentralisation is who is responsible for making decisions about the future of the tech and what happens when people disagree. In that respect Bitcoin is neither decentralised nor neutral. Same as Ethereum.