Yes, mistaken. 3yrs experience at $1000/hr? Not to mention the rates you see are usually firm rates not net to an individual so you have to take out other costs.
Note that this is per equity partner. Many of the largest firms are increasingly choosing to award "partner" status without an equity share as they grow larger, and a non-equity partner will already earn much less.
Most of the top firms will pay a maximum of about $300k/year to 4 year PQE (post qualification experience) in the UK, with UK offices of leading US firms at the top. There may be exceptions for people that make themselves really noticed and manage to land big bonuses. That's generally 6 year after leaving university because of the UK system of training contracts. 2 year PQE's in UK Magic Circle firms can earn about $100k/year.
Some smaller boutique firms in niches may pay substantially more, but they will also generally not take trainees and instead hire away top talents from the leading firms.
To get those kind of salaries you mention by year 4, the answer would be you'd need to bring in big enough clients that your firm is worried you'll walk.