Hey great question!
Essentially for us the timeline between MQL & SQL is usually pretty fast. In our business, anyone that fills out a sales form instantly becomes an MQL. Then our head of sales & marketing will make sure the lead is qualified (right type for services, geographic location, etc) and if they are qualified then they mark them as SQL and that triggers a workflow to our sales team with lead rotation. Essentially, MQL is one additional quick filter to make sure the sales team is spending their time with QUALIFIED leads and not wasting their time with people that have zero chance of booking.
I know what you mean about not using both as I’ve struggled with it too, but it works as a great filtering system so our sales team isn’t wasting valuable time. Please note also that any eBook, quizzes, cheat sheets etc should not be an MQL, that should be into Hubspot as a lead. It’s only the sales forms and missed calls that will automatically mark people as MQL.
Hope that helps!