"Seniority-bias" is the wrong word. It's "skill-bias", or better yet, "tacit-knowledge bias".

The reason why old hands (who have been in the game long enough to be promoted to something approximating "Senior") are so deadly with AI is because they know all the traps/pitfalls to watch out for. Sure, the AIs may become good enough in 5-10 years to have learned all these pitfalls, but make hay while the sun is shining!

"Senior EMs" who are pure HR managers/non-coders will be priced-out of their jobs in an AI agentic world, as (surprise!) you can't report AI agents to HR. Juniors who can use AI effectively will thrive and climbs the ranks rapidly.