Comment by mercutio2

A sizable fraction of people who have many years of experience aren’t good at making you have fewer problems after 6 months of hard work. Those people still think of themselves as senior, so we have to be careful we’re talking about the same pool of people.

But assuming my high performing senior matches your definition of senior, my experience doesn’t really match your approach with “likely better to bring on a few junior engineers to tackle those rather than Seniors”. The people I think of as high performing seniors will do wonders at making a collection of desired bug fixes and required improvements get done and leave the system with, net, fewer bugs. So it’s never better in my book to assign such problems to juniors.

Some juniors do this, at a lower fix rate. Others introduce as many bugs as they fix. Those either get better fast, or get managed out. So in my world, juniors are a resource (“the future!”) we carefully husband, but try not to have many of them on any given team, because the variance in outcome is so much higher.