Hi Alexander, being a IS customer for almost a year now (delivering digital products with marketing automation, online courses), and having tried and left clickfunnels in the process (as landing page platform) I can share my experienced and view on this silly “battle”.
IS is a mature business automation platform and my recommendation is to choose prof. consultant (expensive) help you set up a tagging / campaign system/framework right.
One of our consultants used IS / Clickfunnels for sales pages and works well for him.
We tried CF but left due to overselling by their support on the extend of CF / IS integration level to our specific needs. To me CF is an upsell company and serve many companies good if you buy into CF mindset. I see CF wanting (claiming) to do everything but having worked in internet solution business for +20 years this is a red flag attitude. To me and most succesfull companies going forward will be those having the most open integration business model/attitude.
Instead of CF we now use Wordpress with Thrives themes, which is a bit more technical to maintain but gives 100% ownership and unified design look.
IS is not perfect and seems clunky in some areas. BUT they compensate for very good integration to 3 party solutions to cover for it lacking. So to me IS is a bit more expensive choice in the short run, more technical to maintain, but due to the many 3 part integration and the positioned market leader, we won´t be limited in future possibilities.