The problem with the French fit idea, is that it was developed back in the days when all frames had horizontal top tubes and head tubes were rarely, if ever, extended in height. Back then, the only way to get a tall head tube was to buy an overly large frame. The problem is that the overly large frame would have more reach and probably require a stubby stem. The weight balance would also be poor, with too little weight on the front. The overall idea is too have a small saddle to bar drop, with more reach. That made more sense in the days when the shifters were mounted on the down tube and deep drop bars were common. These days, most bike use brake/shift levers, so it's more common to use a larger saddle to bar drop and spend more time with your hands on the brake hoods.

Today, frame desingers concentrate on stack and reach, although the reach values must be properly corrected to the same stack height, when making comparisons.

Whether one of the new relaxed fit frames is the best choice depends on several things, including your body proportions. If you have long legs and a short torso, you might need the 20mm of additional head tube length, to avoid using too much spacer or a high rise stem. A person with short legs might find a racing-fit bike with a short head tube to be too tall, with a frame having enough reach.

I have long legs for my height, with an 83cm cycling inseam, 73cm saddle height and 169cm height. I like a lot of saddle to bar drop (9-11cm) so I look for a 120-125mm head tube, to get a 140mm total length, with the headset. I use no spacers and either a -6 stem for a 9cm drop or a -17 for an 11cm drop. I use a 110mm stem length, even with my short torso and a lot of saddle setback.

It's all about deciding what saddle to bar drop you need or want, then getting right stack height to produce it, without resorting to a goofy stem/spacer combination.