An all-time great defensive anchor, who can defend every position [DRob], with a specialized scheme that forces long 2s (I'm assuming zone defense is in play here), will negate A LOT of their defensive struggles - especially since Allen and Reggie have the conditioning to chase around Kobe and MJ, and provide some resistance. Curry can just play off Magic and be a nuisance in the passing lanes.
What scheme and defensive anchor does the opposition have to stop Curry-Allen-Miller(or Klay)-Durant from playing behind the arc?
I'd much rather live with the defensive [inabilities] of that lineup, than put forward a lineup with a combination of "shot creation/defense" that can't match MJ, Lebron and Kobe by simply trading 2s - they're three of the greatest 2-pt scorers in history, no other perimeter combination can match them in that department - that's why you need to counter with 3s. At the very least it gives you a fighting chance.
Curry, Allen*, Reggie* (*or Klay), and Durant would kill that team from behind the arc - there's no hope in hell Jordan-Kobe-Bron would be able to keep them from shooting at their typical rates, or even better. They wouldn't be able to double-team them, and they wouldn't be able to chase them around the halfcourt all game long, not to mention they'd need to pick up the defensive slack left by Magic, and Shaq being a liability defending on the perimeter.
Run PnR (DRob + Curry or Allen, or Durant) over and over and over until Shaq can't even run up the floor anymore - that'll have more success than
It's 5v5, so they can't get into foul trouble. If they need to stop the "OP Dream team's" from maximizing their runs/momentum, that can just utilize Hack-A-Shaq.