All the quality soldering standards, set temps pretty much to ~ 350C or lower [ +/- margin for variation within the standards, but definitely not about 400C]. Thus, the fixed temp camp lead by Metcal argue what's to adjust? There are temp scales for different needs, ~ 300C for SMT sized parts, and ~ 400C for large wires or connectors, but none in between. The induction type heat used in Metcal tips are very consistent and constantly adjusts power output to maintain tip temp regardless of the tip load, such as small solder points to points in large ground planes. There is no calibration for such soldering stations. The temp sensor, heater and tip are one piece. Other technologies work differently, but are built around the philosophy of fixed temps.
OTAH, the adjustable camp uses cheaper low tech separate heater units and tips, both of which wear unevenly with use; thus the need to recalibrate. It may be worn to the point the temp provided at the tip is off but the tip is still usable. There is also no sensor on the tip, its on the heater or the tip body, and the scale and adjustment assumes the calibrated heat output of the station is fully and evenly transmitted to the tip. So the adjustment is really there to extend the life of a workable tip, preferably, than to adjust heat for soldering purposes. This is typified by the Hakko 936 or the Weller WES51. If a user adjust the temp to offset the wrong size tip for the heat load or to get better performance from a worn tip then again, those suboptimal technique are allowed by the manual stations, which helps in the short term and for small labs.
There are also stations that are both adjustable and have direct tip temperature feedback and such stations are not calibrated either, and cost more than the Hakko 936.
Both the adjustable have locks to fix the station temps, so the user cannot adjust them which I presume are used in commercial production soldering situations, to emulate what the Metcal folks do.
So who is right? I don't know. But for home lab needs, the Hakko 936 types are the cheapest stations to meet soldering standards, so it provides both the ability to give the lowest heat to solder and maintain tip life, while being the lowest cost. We know for certain were the floor is in terms of modern soldering irons for best outcome, but the ceiling and benefits of moving up depends on what you are willing to spend for a need. For example, the costly stations don't require calibration, so it saves the owner/user the hassle, this can be large if you have many stations and find out the calibration is off when product defects starting popping up or the ISO inspector finds out and cites you; or if you solder a huge volume the difference is tip life between a Metcal and a Hakko 936 may start to become economically feasable.