Yep, air freight is generally by weight, shipping by volume. Electronics are already sent via air, saving $3 shipping on a $1500 item doesn't make much sense. Taking the UK as an example, 70% of non-EU exports by value go via Heathrow. Would expect the value to be similar for China. By volume it's probably low single digits for airfreight, by value likely >50%.

Low value items and very heavy items are currently not viable via airfreight, that's probably where trains can be profitable. If you produce clothes your only options are to either do so in Europe (there's a lot of production in Turkey) and have it close by, or produce in Asia and wait 40 days for every order. Cutting that time for a premium could make a lot of economic sense.