I completely get what you're saying. We've seen many candidates that have expressed the concern of "if I'm going to put X units of time into this, you should also put X units of time into this". A good approach of running a Litebulb interview is to offer to do it in a sit-down session over a call with the interviewer, or to do it asynchronously. When we did sit-down sessions, we offered candidates a choice to just go off and do it throughout the day, whenever they can find the time. 100% of candidates chose to do it async. As it turns out, trying to code something with an interviewer breathing down your neck wasn't a good experience and made them very nervous.

Note that it's an option, not mandatory, to do it async. If the candidate wanted to do it in a sit down session, then we prioritize making time for it to be there the entire session. The reason we offer this option is because devs that have busy lives often can't easily find a single consecutive multi-hour session to do an interview. They have full time jobs, and might have family obligations at home and over the weekends. Basically, the only way to actually do a full onsite interview is to take a day off work to go do the interview. We're giving the flexibility for the candidate to find a chunk of time here, a chunk of time there to complete the interview.

We tested this above approach, because just as you said, we did see a huge dropoff when we just emailed candidates the interview link. After we offered to hop on a call and to be available for support, we saw dropoff reduced to less than 15%.

Also, a good chunk of candidates that drop out of interview processes are senior engineers that can't be bothered with lengthy processes, which is fair. I wouldn't give a Litebulb interview to a senior engineer to begin with. Debatably I wouldn't give any kind of technical interview, actually. If they have decades of experience leading teams at big or high-growth tech companies, those achievements speak for itself. The interview process for seniors should be more geared towards finding a product-team-eng fit, rather than an evaluation.