Author of the paper summary here - my understanding is that XFaaS doesn't run functions that are run in response to user input (e.g. XFaaS does not execute code that fetches and returns data because a user clicked on a button).
The x-axis is size of trade, and the y-axis is % of trades at a specific size. ExRates had _many_ large trades, which shows up as a significantly different distribution than other exchanges like Coinbase/Bitstamp/Kraken (which had many small trades, and a long tail of larger size trades). See slide 42-44 here: https://www.sec.gov/comments/sr-nysearca-2019-01/srnysearca2...
100% - although this time around there is (in my opinion) _a lot more data_ [1] that regulated markets (like CME bitcoin futures) drive price discovery.
[1] There was data back then too, it just wasn't received.
Neat and funny that they have an uncited figure (the one with the six exchanges with wacky trade size distributions) from research that we did while I was working at Bitwise.