This is true. I have around 6 years of experience and when interviewing recently I tried two approaches:

1) Not preparing myself by reading on data structures and algorithms. Just relying on my solid experience to carry me.

2) Spending couple of hours evening before interview to quickly go through data structures (array, linked list, hashmap, stack, queue, binary trees), algorithms (searching binary search trees, merge sort etc) and writing quick implementations of couple of most common algorithms you get asked about during interviews (just to have fresh "muscle" memory to be able to quickly write an implementation on the whiteboard with confidence).

Approach 1) did not really work well for me. After I switched to 2) the interviews got much better for me and offers started coming.

So I'd suggest even if you are very experienced and have a decade of experience, don't rely on that being enough. Spend a day before interview refreshing your memory on computer science fundamentals, try to memorize Big O cheat sheet. And you will be much more likely to get offer.

Even though I've not been in interviews for a couple of years now I still read from time to time something on the basics of algorithms and data structures to keep it "fresh" in my mind.

I go from re-reading Skiena's Algorithm Design Manual (I prefer his writing style over more formal textbooks like CLRS or Sedgewick's) to a more easy to digest piece when I'm really not in the mood for formality (last one was this week with "A Common-Sense Guide to Data Structures and Algorithms").

It helps me to refresh it with different styles of writing as I can go from a very broad overview to the details if/when I want but I always have the basics in my head.

I hope I won't go for another interview soon though, it's really tiring, I have 12 years of experience now and I still dread just thinking about going through the process again.

I think having a tier 1 college degree matters the most even in getting an interview, atleast here in India. This is from my experience of seeing increasing job posts having tier 1 college degree as requirement and colleagues I know having good college degree having no difficulty in getting interviews(github code, portfolio etc really doesn't matter)

Not true for a 5+ years experience. The scene is changing fast. Github is a plus and hacker rank interviews are getting adopted in almost all new startups.

It's because the vast majority of candidates, including a lot of very good ones, will do none of those things.

Work will have much more in common with said open source efforts than with all those algorithmic challenges though.

A good chunk of these people will be good engineers that cannot talk about or show the stuff they worked on at their previous job. And those places specifically ban them from making apps or working on open source and they will be hard workers that work 40-50+ hours a week. Maybe they have kids too.

How do you interview these people?

I agree, algo interviews are annoying and I wish it wasn't there. If it wasn't it would make switching jobs a lot faster. But thats what it is. The suggested alternative of portfolio work has it's own problems, the same with homework problems.

Unfortunately, even places that have you write code with the internet still have an algo inteview or two.

I had an interviewer ask my for some code samples. Conveniently it was the day after I accepted another offer, but that was a definite no bueno for me, I don't contribute to open source, and I was hardly going to send them some code samples from my previous job.

Sure, but you need to be able to produce a work product example of some sort in lieu. Most people can.