I’m not describing how the world should work, just how it does when outsourcing IT to consultancies (which can work anywhere from successfully to very unsuccessfully)
A good strategy is to hire a team, get a few consultants who have literally built the same system down the road, and use that blended team until 2.X release.
That way you a team that has made a thing already (and often consultants are just as passionate about their work too!) ready to build a better 2.0, plus you keep responsibility and control.
Some orgs may not know how to hire. I think here, competent (and well connected) consultants can help, and maybe source from their own networks, but we're back to the dilemma of which consultants to trust. And let's not speak of recruitment agencies :)
Hint: the rivalry will make it also expensive (extra meetings, defensive bullshit). But you will end up with what you wanted, at a price.
Some orgs just don't have the in-house capability to do this, so they seek a consulting firm... oh wait.
Edit:
I guess the strategy is to hire technical staff, keep them around a few years until you can be sure they can deliver on projects and understand your existing systems and processes, and then embark on the larger project to transform those systems and processes.
Alternatively, shop around to find a consulting firm that is motivated to have good long-term outcomes. Probably a smaller operation, that has good word-of-mouth reputation, but doesn't have an established brand to fall back on.