Doesn't the lockstep go away after only a promotion or two when the attorneys get promoted beyond senior associate? I guess that's still the better part of a decade, though.
The promotions are based on business case, especially as you get senior. To make a business case for partnership practicing technology law at BigLaw you need to have a decade or more of doing that as an associate, where you get paid more or less the same as everyone else at your level. In fact it can be harder to meet your targets / make your bonuses because technology law tends to be faster moving than other areas so proportionally more time needs to be spent on professional developer, as against fee earning.