New Zealand ran up 401 for 6 in Bengaluru last Saturday - but still lost to Pakistan, who were probably helped by the rain that curtailed the match.
As I write, Trent Boult has 207 wickets from 112 ODIs, while Mitchell Starc has 229 from 118. There's someone else in the current World Cup who's very close to averaging two per match: Shaheen Shah Afridi currently has 102 wickets from 52 (he was actually averaging exactly two per match before going wicketless against New Zealand in Bengaluru at the weekend).
The short answer is yes: as I write there have been just seven partnerships of 250 or more in men's World Cup matches, and David Warner was part of two of them. He put on 260 for the second wicket with Steve Smith against Afghanistan in Perth in March 2015, and 259 for the first with Mitchell Marsh against Pakistan in Bengaluru in 2023.
Sri Lanka's calamitous collapse in Mumbai last week - Kusal Mendis and Charith Asalanka were out for 1 after ducks for Pathum Nissanka, Dimuth Karunaratne and Sadeera Samarawickrama - was actually the worst return by the top five in the batting order in any men's one-day international.
You're right that Ireland's Paul Stirling leads the way here, having played official T20Is against 29 different countries. His team-mates Mark Adair and George Dockrell come next with 26; Andy Balbirnie and Harry Tector have faced 25 different opponents, as have Rohan Mustafa and Ahmed Raza of the UAE.
Steven Lynch is the editor of the updated edition of Wisden on the Ashes