I think this would be a fair and effective interview system:

1) College graduate: Keep the traditional algorithm programming tech interview. But allow the use of a laptop (no whiteboard)

2) 2 - 7 years engineer: Require a github side project or give a home coding test. Interview will focus on discussing the project implementation. Also ask them to add a simple feature.

3) 7 - 15 years engineer: Ask them to come to the office and show them some bad code from the company source control. Ask them to explain why it's bad and to refactor it to something better.

4) Express route: Instant offer, no interview. Only "interview" is by a VP and it's more about trying to convince the candidate to join the company instead of the other way around.

The first 3 scale according to typical life situation and industry experience. The amount of free tend tends to decrease from college graduation to 30's and beyond. For example, a college graduate has lots of free time. Someone in their 20's has less, but still a significant amount. 30's and beyond tend to have little free time due to family responsibilities.

But the interview styles also match what they should know by that point. A college graduate doesn't know anything about real industry coding so the typical algorithm coding interview is ok. Someone with 2 - 7 years experience should be good at writing lots of code. But they don't yet have the experience to know that sometimes deleting code is better than adding more. They also don't have enough experience yet to read code well and refactor, their "code smell" sense is not yet developed and they think adding more code is the solution to everything. An industry veteran of 7 - 15 years should be able to read code well, spot all the issues, and be able to refactor into something better. These skills can only be gained after years of experience.

So the 3 interview styles scale well according to the free time they are likely to have and testing whether they've really grown as an engineer. The last one, the "express route" is reserved only by referral from the company's best engineers. For example, if the company has this tech ladder:

junior engineer, engineer I, engineer II, senior engineer, senior engineer II, principal engineer:

Then only senior engineer II or above AND being at the company for at least 3 years would be allowed to make ONE express route referral per year. The reason is that an engineer has to be in the industry for a while to meet other good engineers. And 3 years is enough to learn the company culture. This express route system effectively would give a competitive advantage over other companies. For example, imagine a very good engineer who is already employed. They are busy and don't want to go through any kind of interview process. But if they are given an instant offer, that greatly reduces the barriers for them and they are much more likely to seriously consider switching to the company. The main idea here is that good engineers have a lot of options but not much free time to interview, your good engineers should know a few in other companies, so the express route is a way to get more good engineers who would usually not consider moving because they don't want to spend time interviewing.