If I were to steelman your position,
for now, people need to be a good dev to make the most out of the LLM ecosystem, and the skill of prompt engineering varies person to person as well. I could see an exceptional dev outputting not just more than they used to but with their improvement relative to themselves being much higher than the average improvement other devs gained. In that scenario, yeah, salaries could still increase despite the role being AI-assisted and despite the LLM tools costing these devs' company money every query. Skill varies anywhere between "vibe coder" all the way up to the highest position that still codes at your company, and familiarity with how to leverage LLMs the best can vary that widely as well.
Right now, the name of the game is making sure your LLM has a good action plan before letting it attempt to fix a bug or refactor or add a feature. Devs with more experience know what to ask Claude to do whereas a greener dev doesn't know the questions to ask, leaving Claude to guess right sometimes and wrong sometimes. Simply put, if a dev doesn't know to ask for something, there's a bigger chance the LLM won't care to do it. And if there's some nuanced, tricky aspect to the code not described to the LLM, the LLM might burn a lot of tokens to reach a bad solution. A good dev might give more clues and hunches and more context to fine-tune the prompt so that it almost definitely succeeds whereas a greener dev doesn't have intimacy with the system yet, needing tips and descriptions of subsystems themselves before they could pass it along to Claude. By this stage, people also differ in their skills with the various tools in the ecosystem. Power tools do a lot more in the hands of a seasoned handyman than in the hands of an eight-year-old after all.
However, the better LLMs get, the less differences like this will exist, and ideally, every dev will approach a similar amount of productivity. Salaries aren't reflective of how much profit a worker produces in the company (unless you are the CEO or a little below them or maybe have some stock). Supply and demand drive salary. If something nearby AGI arrives tomorrow, by definition, almost any two devs will provide similar value at which point teams will downsize, yet productivity will hold steady or increase. They will downsize to save some money since we live in a brutal world where workers have no loyalty to a company, and a company has no loyalty to its workers. Pensions are a relic from the past. After all that will happen, a large group of qualified devs will be searching for jobs, so they can remain in a home with food in it. Companies will see tons of resumes flowing in all by AI-assisted devs that can do the job.
The companies will then do two things: Offer the hired devs a transfer to AI-assisted dev for less money or else while also interviewing all the ones that all the companies fired, giving them that same AI-assisted dev salary to everyone in the picture. And they will have calculated the proper discount off the old full salary using some kind of economic equations. Then the wildcard happens: some of the ones needing work urgently start to offer their services for even less than the company is. It's a spiral downward until the salary becomes so low to the point where a dev would rather be an ex-dev doing something else that is more relaxing and also still paying them enough money to survive. No reason to do tough coding work, it'll still be tedious with stronger LLMs. Comfort and relaxation will prevail for many as they no longer feel the salary justifies doing the work.
And at the top, assuming AI costs do not exponentiate, they will be making more money than ever before since they downsized teams, slashed salaries, and got hired at even lower salaries than the slashed salaries. (There will still be a premium for knowing the systems like the back of your hand without need to ramp up before adding value, so you'll get paid more than a new hire.)