I am running step-and-a-half on several bikes as follows

Bruce Gordon touring bike, 44-36-22, using a Shimano XTR FD-M900 (old 8 speed from about 1994, designed for maximum large chainring of 48T, minimum difference of 8t between and middle chainrings, and a maximum capacity of 26T large to small chainrings).

Co-Motion Touring, 46-38-24, using a Shimano XT FD-M735 (old 7 speed from early 1990s, designed for maximum large chainring of 48T, minimum difference of 5t between and middle chainrings, and a maximum capacity of 26T large to small chainrings).

Santana Visa Tandem, 52-44-28, using a Suntour XC Pro FD-XP00-GHX (old 7 speed from ??, designed for maximum large chainring of 48T, minimum difference of 8t between and middle chainrings, and a maximum capacity of 24T large to small chainrings).

The trick with all these older front derailleurs is they have a small inner plate. Yes, they may not have as crisp a shifting as newer derailleurs, but I have good shifting with non matching chainrings. These and other front derailleurs from the same era are available used on e-bay. Not much can go wrong with these so even used are perfectly functional. I also understand that of the modern FD, the Shimano FD-CX70 works well.

The problem can be matching older derailleurs with brifters. I am using Campagnolo Chorus shifters and they work perfectly shifting across the full triple crankset. If using bar end shifters, the front shifter is friction, and are ths compatible with any and all FDs.