There's no other players from the OKC stepping up, unlike with the Mavs where their bigs have stepped up. SGA is good as we can see on his output, but him alone carrying the team would give them a slim chance of coming back. Well, a win in game 6 would bring this game to 7, but how sure they are they can win game 7? I don't know, the OKC have the chance to take the lead as they are at home, but that two losses at home resulting them to be down 3-2 in the series.
OKC only shoots 25% from 3, it was suppose to be their strength, so when they struggle in that area, we know they'll likely loss.
their average this season was almost 40%.
https://www.statmuse.com/nba/ask/thunder-3pt-percentage