The "primary" and "secondary" street network of Paris, respectively. Main streets are continuous and connect clear nodes, the side streets are all very short and involve dead ends: you can't go anywhere without having to take a lot of turns.

Yeah this is a major point. In a city like Paris where there is an extremely obvious street hierarchy, main street bike lanes are critical and side street bike lanes almost useless, whereas grid cities with parallel routes could probably get a bit farther with side street lanes.

Do you think this is the type or corridor that could benefit from a tram? Or is the catchment area not dense enough?

I grew up in California suburbia and used to dislike cities because I mostly experienced them behind the wheel of a car and found it so much less convenient than doing things in parking-rich suburbia.

Yeah, I very often find myself leaving my place with no bag at all and only with my phone, wallet, and keys. When I'm sightseeing or showing American friends around Paris, we might walk more than 10km or even 20km but it's always broken
up by a stop at a terasse/café to drink/use the restroom/chill.

I live in Greater Paris and used to live in central Toulouse and it's true that I rarely carry a water bottle on me (and I don't think that's uncommon). I guess my trips are either short, and/or involve a destination where water is easily accessible (work, restaurant, gym, bar, café).

I'm not entirely sure this is true. At least in France the state has expanded massively since the 70s due to the need to deal with the pension and healthcare costs of an aging population. For that matter I think full universal Healthcare was only reached under Jospin in the late 90s or early 2000s.

French municipal fragmentation is also usually really bad. Paris, Lyon, and Lille are tiny.

I agree with your main point, but I think the quasi-pedestrianization allowed by trams and the "street renovation" effect has been cited as a big driver of the French tram revival. You don't see it much in Paris-IDF but it's a big part of the public space in Bordeaux, Montpellier, Strasbourg, etc.

Are there any advantages to it? I've been wondering why T3 in Paris has some lateral sections.

This is a really cool map. Did you make it yourself?