It's not a 0% bonus and then 20% when full partner. It's about 1% year 1, 3.4% year 2, 6.6% year 3, 10% year 4 and then 20% for any work starting after 4 years so not as bad as the math above suggests. But I totally see your point, there is a delayed payback that requires a 10 year mindset where it becomes really worthwhile, and close to break even/grey area at 6-10 years. Before that totally depends on starting pay vs the competition which will vary a lot from local market to market and makes a general comparison almost useless. You're also right in that the "equity" is generally the ability to work with a higher pay rate ie bonus in the long term. Still, I find that these are all rather self evident math problems depending on a person's goals, where they see themself long term etc and are similar with any difficult decision to join a partnership track private group (buy in, hourly differential, years to partner etc).
I would also be very concerned as a potential applicant if comparing CMG pay which has a huge downward market pressures as your labor has to make profit for the shareholders and pay will be pushed as low as the company can get away with in the future while still maintaining staffing. Better comparison would be to the various private groups around, which have a huge variety in compensation/partnership models and share profits. In all honesty, I knew which geographic location I wanted to work, and picked a nice financially stable hospital with a well run group that happened to be Vituity. Happy with that choice personally and nice to know that if I wanted to move or there was a contract issue then the partnership level would follow me to another Vituity hospital/contract. I would not want to be a CMG/locums doc in today's market though, that's for sure.