In a very crude way, sales is about landing new deals or expanding. Customer success is about securing renewals for existing customer and increase adoption, prevent churn. It is a post-sales role.

IIRC (It's been a while since I've worked with their teams) Customer Success was handled by the 'integration support' at Docusign.

If I -also- recall, When I did an Auth0 integration (a few years before that) I worked with a similar 'Customer Success' specialist while evaluating for an integration.

I think this is the trade-off that's happening; By putting integration support under a 'marketing' budget rather than a 'support' budget, it allows for a happier adopting customer base.

I must add however; those examples stand out to me not because it was 'sales-y' but because they were extremely memorable times of a vendor team working very hard to lead our teams into a pit of success. The best analogy I can think of is the difference between someone on a call giving a vague phrase you have to search through API docs for, vs a direct link to documentation complete with verbose-yet-sane examples.