Even that requires a tailored suit, not an off the rack one. I just can't see the dichotomy the author mentions. Suits are clothes and they can be modern or not just like anything else. The differences are that older clothes were generally made to last longer, and that suits can be tailor made. But suits can be also cheap and low quality, they can be ill fitting, and here it doesn't matter if they're old or modern.
As for comfort, look at clothes you'd wear for relaxing on the couch or for extended periods like a long flight. A suit can be comfortable for a suit but otherwise they're mainly a matter of looks rather than comfort.
Suits generally are pretty comfortable though, other than the shirt and tie which give me something close to claustrophobia. Some of my favorite pants for lounging around the house are suit pants.
After wearing suit and tie for decades, and liking it as a work attire, I can't imagine how a suit can be more comfortable than clothing that doesn't have to follow a strict design so is free to focus on comfort. Like a track suit.
Business suits are limited by the choice of fabric and the specific cut. To make them more comfortable they would have to compromise the design, and the fabric would need to change.
Comfortable clothes usually follow the movement of the body with little to no resistance, either by stretching with the skin (tights, never wore them but I hear they're comfortable) or baggy clothes, usually with synthetic fibers.
You can find casual suits that are basically track suits with a business suit general look but I wouldn't conflate them.
Honestly, I don't mind wool. I've never felt it to be scratchy, but I hate polyester, which I do find irritating. I don't wear suits regularly because I hate collared shirts and I'm not a tophat capitalist, but I've never found them to be uncomfortable.
As for comfort, look at clothes you'd wear for relaxing on the couch or for extended periods like a long flight. A suit can be comfortable for a suit but otherwise they're mainly a matter of looks rather than comfort.