Actual Bluetooth is slow, 1.5Mbit or so, depending on the implementation. You wouldn't transfer large amounts of data that way. Maybe a photo, or smallish files. But, as the other poster noted, Airdrop uses Wi-Fi direct now so it's at wifi speeds.

Modern Wi-Fi 6 (what is in the new iPhones, even in the older iPhones) is theoretically much faster. Gigabit+ speeds. In practice, you can expect similar or faster speeds vs. USB2 over Wi-Fi. If it's ad-hoc from iPhone to iPhone, it should be much closer to theoretical max since they will be in close proximity.

I’ve seen both AirDrop and LAN over WiFi reach a steady state at around 55-60 MB/s in ideal conditions, which is remarkably similar to USB 2.0. That speed is only reached when the devices are stationary and close to each other though, any movement causes a temporary drop since wave compression or interference presumably results in signal degradation and some sort of checksumming to occur. Also I can’t recall the specifics but AirDrop only uses Bluetooth to negotiate the connection. The underlying transmission uses peer-to-peer WiFi, so it’s no surprise their speeds are similar to each other.

Incidentally, I’m sure there’s a myriad of practical reasons why it would have been too early for Apple to go entirely portless, but funnily enough as it turns out, a decrease in transfer speed compared to USB 2.0 over Lightning wouldn’t have been one of them.

AirDrop only uses Bluetooth for handshake and configuration. Data is then transferred over Wi-Fi Direct.

Airdrop negotiates a WiFi connection using Bluetooth but does all the data transfer at WiFi speeds.

USB 2.0 Hi Speed is 480 Mb/s

I get about that with my 13 mini on my WiFi 6 AP.

BT 5.x I have no idea.