Not a Pages power user, so I may be missing some nuance here, but why would
...followed by
...be "mighty slow and clunky"?
Anything else is going to depend on you visiting the body text and then every text box in turn, since the find and replace in Pages has neither AppleScript nor Shortcut support -- and that's before getting into how to find and change the text. Even if you've multiple searches to do, that's going to be way trickier than using KM to automate the built-in dialog.
Edit to add:
So here's an AppleScript to find'n'replace pairs of terms across the whole(?) of the front Pages document. It's working on a short document, but see this thread for problems you might stumble across.
set pairsList to {¬
{"(", linefeed & linefeed & "("}, ¬
{")", ")" & linefeed} ¬
}
tell application "Pages"
tell document 1
set thePages to a reference to every page
repeat with eachPage in thePages
tell body text of eachPage
repeat with eachPair in pairsList
set (every character where it is (contents of first item of eachPair)) to (contents of second item of eachPair)
end repeat
end tell
end repeat
set textItems to every text item
repeat with eachTextItem in textItems
tell object text of eachTextItem
repeat with eachPair in pairsList
set (every character where it is (contents of first item of eachPair)) to (contents of second item of eachPair)
end repeat
end tell
end repeat
end tell
end tell