Can't comment on PSV and Ajax, but Rangers also reached a European final in 1967, losing 1-0 to a Muller and Beckenbauer powered Bayern, showing the strength of the league then. So Celtic's '67 treble has to be up there, at least anecdotally. Obviously for a proper claim you'd have to sit through a lot of old games which I'll pass on haha
Can't comment on PSV and Ajax, but Rangers also reached a European final in 1967, losing 1-0 to a Muller and Beckenbauer powered Bayern, showing the strength of the league then. So Celtic's '67 treble has to be up there, at least anecdotally. Obviously for a proper claim you'd have to sit through a lot of old games which I'll pass on haha