No, they didn't. It was straightforwardly unsafe and broken, the heaps of effort that went into supporting it were largely just to paper over that fact. It's no accident that the other browser vendors went along with dropping support so quickly after Apple did.
The reason given for blocking Flash on iOS at the time was it's too cpu intensive on mobile, which impacts battery life. Not that it was "unsafe and broken".
The main reason other browsers stopped supporting Flash was websites stopped being built with Flash because iOS didn't support it, and a lot of people thought that mattered even though iOS had (and still has) a small market share world-wide.
