The first of course, is the STUPID RIDICULOUS amount of energy it takes to mine bitcoin.

This is how Bitcoin is supposed to work. The waste of energy generates security of the underlying chain. In order to maliciously change the protocol, any attacker must waste an enormous amount of energy in order to double spend or make protocol changes. With proof of stake blockchains, a super staker or staking cartel can strong arm changes just by having a majority / large amount of staked coins. Steem wasn't able to prevent Justin Sun's hostile takeover from enacting chaos and leading to the chain split. Granted there is little incentive to undermine the monetary policy of PoS chains, the fact that these changes are more easily possible is a potential security issue. The inefficiency of PoW was unintuitively part of the innovation that made Bitcoin work.

I think to consider the first implementation and iteration of a new technology to be the "end-all-be-all" is at the very least, hubris. Think of it this way; The Model T was the first major mass produced vehicle ever made.

Bitcoin wasn't the first digital currency and is a synthesis of different technologies that preceded it. The underlying protocol is also continuing to change in order to better improve the protocol. Comparing protocols to motor vehicles as a metaphor doesn't really make a lot of sense because protocols are a set of rules that dictate permissible behavior rather than a product that is obsoleted after time. Bitcoin is more similar to say a constitution rather than a Model T. Not to say there aren't better constitutions out there, but the amending process makes constitutions robust in ways that single-use products aren't.

Developers are stuck with what they have, and it seems rather infeasible to say, get the ENTIRE NETWORK to fundamentally change after the fact.

This is probably Bitcoin's strongest weakness, but I would argue that Ethereum suffers from this issue much more significantly (and other protocols do as well including Hive). It really depends if Bitcoin is clean and sturdy enough as it is to be a sufficiently concise and feature-rich layer to be built on. I think the all-in-one-layer approach doesn't work with protocols as they become too complex and cumbersome and more vulnerable to bugs and harder to maintain and grow. As a software engineer, there is nothing worse than over-complicated behemoths. Even if Bitcoin struggles with this issue, all blockchains (that behave as decentralized blockchains) will also struggle with the issue. Protocols are never universal so there will always be some deficiency in the protocol (Bitcoins transaction speed, PoS staking attacks, Steem/Hive incentive structures).

there are a lot of points here that makes it seem absolutely inevitable that other blockchains and tech would eventually arise to challenge Bitcoin.

As Bitcoin is structured and designed, I don't really see comparable technology that "challenges" Bitcoin and sufficiency addresses all the problems that Bitcoin is solving. That doesn't mean that parallel and collaborative technologies can't exist. I'm not a Bitcoin maximalist by any means, but Bitcoin is the only coin that I have confidence can survive the next twenty years based on what technological problems it solves. I haven't reached that point with other coins, but that doesn't mean I haven't dabbled with other blockchains. Maybe I have yet to understand how they really work. At one time I thought that Bitcoin was outdated from many of the same reasons explained in this post but through time, experience and familiarize myself in the space I have begun to understand that perspective. It would be short-sighted not to try and understand the new technology and figure out what works and what doesn't work with that protocol. The biggest issue with the space is the bias those monetizing innovation. Too many projects are focused on making money rather than developing with the spirit of innovating and experiencing. Coins like TRON that plagiarize whitepapers and rely on hype to generate speculation aren't moving us forward and they might be wasting potential money in the space. So in some sense I can understand that perspective from Maximalists, although I encourage the development of technology both as a layer cake on top of Bitcoin or in the form of new protocols that we can trial new ideas on.