Network adapters definitely need speeds faster than USB 2.0. You're definitely not going to get gigabit speeds on a raw bandwidth of 480 Mbps. I think capture capture devices that can take 1080p or higher are also demanding high bandwidth for low-latency monitoring.
Regarding the power thing, I believe the USB-IF basically said "do whatever, as long as you don't blow things up." After all, the original USB 2.0 spec only allowed for 0.5A, but we have 2.0 ports that deliver more than that.
USB 3 is compatible with 2, as long as it is a USB port, 3 can be used.
But 5Gbps is really too fast compared to 480Mbps,
With the popularization of digital media, the capacity of high-definition videos, game programs, and digital photos are basically a few GB or even dozens of GB. If you continue to use USB2 to transmit, it is really too slow.
For people who often transmit large-capacity data, 3 is necessary, if not needed, 2 is enough.
You are right in your approach. The main advantage of USB 3 is in data transfer speed, small advantage in power max. if you have and use an external power adapter.
USB 3 higher speeds are available only if the entire set is USB 3. That is, for one USB 3 port, the port, the cables used, and the device attached on the end all need to be USB 3. If any one is not, the system WILL run but at old slower USB 2 data rates.
To keep track of the changes in USB 3 naming, here's where we are now, I think (early 2021). ALL are named now as versions of USB 3.2 Genxxx. They all use the same ports and connecting cables, but there are two main types of connectors used. The Type A connector, which looks a lot like the original USB 2 type A, has a rectangular metal shroud containing a support against one side like a piece of circuit board but carrying NINE contacts. The male plug on the end of a cable from a device has four contacts as strips on the support horizontal surface (just like the USB 2 connector) plus five dot-like contacts on the front tip face of the support. The socket in the host (computer or whatever) has the four matching strip contacts easy to see, and the matching five dots are on the innermost REAR surface of the socket. The second connector style said to be superior for reliable fast data transfer is the new Type C one which is much smaller with a rectangular shroud with rounded ends enclosing a central support strip that has surface contacts on both sides. Both types of connectors are part of the USB 3 system, but the Type C one is preferred for the fastest speeds. Those speeds now include:
USB 3.2 Gen1: max 5 Gb/s
USB 3.2 Gen2: max 10 Gb/s
USB 3.2 Gen2x2: max 20 Gb/s
Typical device speeds.
As posted above, mice, keyboards, many items are slow - USB 2 is good enough. Video device (cameras, capture, etc.) probably fast enough to need USB 3.2 GEN1 Network interface - IF you are using an external network USB device, and not the port built into your mobo or a PCIe network card - should be on USB 3.2 Gen1. VERY few wired networks exceed 1 Gb/s ("Gigabit Ethernet") Storage devices - mechanical HDD's (with rotating disk and moving heads) ALL top out at about 2.0 to 2.5 Gb/s data transfer, limited by the mechanical components. Although they are rated up to SATA III at max 6 Gb/s, that is the rating of the max data transfer capability of the communication interface, and NOT the rate the device hardware can actually find and deliver data. Storage devices - Solid State Drives (SSD's) certainly can get close to the 5 Gb/s rate of USB 3.1 Gen1, and a few may exceed that and benefit from a Gen 2 system.
Currently I know of no devices that can provide or accept data at speeds exceeding 10 GB/s. But the Gen2x2 version of the interface has been deployed in anticipation of such developments in the future - when they arrive their performance will NOT be limited by the communication interface system. USB 3.2 Hubs may benefit from using Gen1 or Gen2 ports. Recognize that, when you use a Hub, ALL of the devices attached to that hub must share that single USB3 connection to the host port. So if several such device are faster ones (see above) and all working nearly simultaneously, the aggregate data transfer rate along that link will be faster that the rate for a single device. I really suggest that, especially for USB 3.2 Hubs, the hub should have its own power supply module ("wall wart") to ensure that every port on the hub has the full 0.9 A max power available to its attached device. Without that, trying to share 0.9 A from the host port to ALL attached devices risks under-powering them.
A side note on power, not part of your original inquiry. The small Portable Laptop drives now on the market are all designed for use on USB3 systems. They certainly benefit from the data transfer rates of this system vs. the slower USB 2. But the big difference is power. There were virtually NO such drive units for the USB 2 era that could work with the 0.5 A power limit. Those drives either had their own "wall wart" you needed to use, OR they came with a special two-headed USB 2 cable that you had to plug into TWO separate ports of the host computer to get enough power. The new USB3 units do not come with such accessories because the power limit of 0.9 A on the new ports is sufficient. BUT they often are promoted as "USB2 compatible", which I find deceptive. They can ONLY work when attached to a computer USB 2 port IF you can arrange to supply the power they need - certainly more than the 0.5 A the USB 2 port can provide. For example, I has success with such a unit this way. I bought a powered USB 3 Hub (with "wall wart") and connected that to a computer host's USB2 port (cable for that can be either system). Then I plugged the new USB 3 Portable Laptop Drive into the HUB with a USB3 cable, so the drive gets the 0.9 A power source from the Hub and can communicate with the Hub at the faster speeds. The speed thing does not matter, however, since the connection from Hub to host is USB2. The point is, this DID work becasue the USB3 drive unit got the power it required from the HUB, and not from the more limited USB2 port of the host.