You are saying never start a startup? If you don’t want to take a risk on a startup, you’re much better off taking a salary job than trying to get a high hourly contracting rate.
Strange analysis, these numbers mostly don’t add up. People contracting at an hourly rate almost never get constant consistent work, otherwise you’d get hired on a salary. You have to spend half your time looking for work, and you’re not accounting for that at all. At 400 hours/month, you are suggesting working 90 hours per week for 365 days per year. Having worked this many hours before for stretches, I know first hand this is a recipe for complete and total burnout and depression within a few months. And even 90 hours per week at $150 per hour doesn’t add up to 70k/month, it’s 60k/month. 2x/3x engineer is usually referring to productivity, but not pay. You generally can’t increase your pay by being more productive. Pay scales that you’re talking about ($300/hr, $450/hr, $600/hr) are extremely rare in engineering and come only with niche software markets. Almost nobody is making hourly rates like that, there’s nothing basic about it, this is an unrealistic goal.
I'm not sure this makes much sense. If you work for a large corporation you can easily make 100K+ a year and work a very reasonable 40 hours or less a week and live off of 4K a month.
Unless you're actually realizing those gains and earning 300K a month, you are not "basically making 300K a month for 4K cost". You are making 0 dollars a month for 4K cost.
Further, if you think that it will pay you back in full in the future (instead of making the money right away), you will have to invent a wildly successful product and/or customer base to backfill the pay for all the previous hours worked. Realistically, you'll probably make nothing for your first year unless you start with a plan to secure funding. You'll also bust your ass for a year while losing money in the hopes of a reward in the future. I know they say time is money, but it's not money the way you seem to be equating it here haha.
If you hourly rate is 150$ (in the market), and you can work 300H a month (including weekend) (It should be 400 hours - 13 hours a day).
Than you are basically making around 70-100K a month (in value), but paying only 4K (in cash, your living expenses).
Of course, if you are 2X, 3X , 4X engineer , you are basically making 300K a month for 4K cost.