I’m not sure I agree with that
You see many top players today taking full back swings close to the bridge hand and doing well with the tight pockets
Chris Meling and fedor Gorst come to mind
Yes - but the big difference is that most of the great players today who pull the cue further back on the backswing do not have much shoulder integration into their stroke - it is mostly an elbow only pendulum swing.
So they are clearly more compact and robotic. They get the timing down so that the elbow pivot allows for max velocity as the cue strikes the cue ball and that creates the action needed without extra effort or moving parts.
Some, like Meglino, as seen this week, are mostly just forward motion of the cue with little back swing - he uses a short backswing almost exclusively when he wants to draw the cue - watch closely on different shots.
There is NO doubt that the old Brunswick GC 4 7/8 standard and the Cenntenial/ Anniversary model were 5+ — allowed for way more leeway in stroke mechanics to still play very very well.