The key drivers for this: complexity of the product being sold, length of sales cycle, and stage of the business. It's at least a 3-dimensional matrix to map when an organization may actually do better with a smarketing department vs keeping those functions separate.
And, even if some version of smarketing is right for you... the implementation of that is a curve, it's not binary. You already have a clear view of the two extremes (pure smarketing vs purely separate), but imagine if the organization was large enough to have a President of Smarketing, with a VP of Marketing and a VP of Sales under her/him? Or what if the same person wore both hats, but ran two mostly separate groups? Strongly unified leadership and goals can affect the way the two groups work together.
In general an organization selling very simple products, with short or instant selling cycles, will want to make sure that the entire customer "experience" is very polished (yes, you are going to say that is always important). With a longer sales cycle there will be a relationship with the salesperson. That relationship is what will eventually close the sale, and small miss-steps or miss-alignment with the perfect marketing message get a little less critical to conversion. But that requires a large enough average spend to justify direct sales involvement, etc.
If you could only pick one of the following to focus on, which do you think would do more for the specific product you are contemplating?
- Have great relationships between the salespeople and the prospects.
- Have a fantastic on-message sales funnel perfectly consistent with brand and marketing strategy?
I think you could pick a product at random and see it probably leans toward one or the other (most of the time).
I hope that was better than just saying "it depends".