All engineers should be spending more time "planning" than "doing".

Even before LLMs, the coding tasks were less than 50% of the time spent on all my Jira boards in the past 15 years. It makes perfect sense that they are assigned based on available capacity. By the time the coding begins, it's already too late to worry about implementation.

You're right that small tasks are trivial enough to be assigned to anyone. That's the point. That's how it feels to work on the "good" projects regardless of complexity. Planning a complex project should result in more tasks, not harder tasks. Your epics and stories can sometimes vary in points, but your tasks should not. A primary goal of the planning phase is figuring out how to keep them as low as you can. The points stop being meaningless when you think this way. They tell you where things are too lumpy. You throw more planning time at those lumps.

If assigning to a senior produces better code, you're not spending enough time planning ahead.