My kayfun 5 has been in constant rotation for almost a year now, really like it, and use it in almost the exact opposite of how you use it, I keep the airflow wide open on the restricted lung hit setting. Right now I have a .3 ohm ish fused clapton in it, and vape it around 40-45 watts depending on the juice. Other times I'll use a SS316 spaced coil with temp limiting/control.
It's a great tank, no matter how you use it, low airflow MTL style and higher ohm/lower wattages, or restricted lung hit lower ohm/higher wattages. I don't know that I agree 100% with you that it is better with the MTL reducer and lower wattages, but those opinions are a bit subjective, and I respect your opinion and am glad it got you to think differently about your vaping style. The KF5 also changed my vaping style a bit too, from dual coil high airflow RTAs, and RDAs to now more restricted lung hit single coil RTAs, and restricted airflow RDAs.
TLDR; it's a versatile, and great flavor RTA.