Beast mode has always been a bit of a marketing gimmick rarely justified in actual combat operations.
There are basically two extremes where you might want to employ such a load out, and it’s not particularly advisable to go with such a load out even in those extremes.
On the one end, you face a peer or near-peer and expect to be fighting the biggest air battles in history with hundreds of top fighters from both sides involve, so beast mode gives you more shots in such a target rich environment and maximise the number of missiles your side brings to the fight.
The problem is you cannot expect opfor in such a top level fight to just throw planes into the mix like a lemming rush with no consideration for tactics, support assets and discipline. So if you just expect to be able to fly in, mass dump missiles and call it a day, you are just going to end up wasting masses of missiles for minimal kills as opfor easily jam and/or dummy your alpha strikes.
What more, you are putting your own planes at greater risk in such fights with such a load out because you are either staying committed for far longer than you should be trying to spam all your missiles and/or you are going defensive with a far heavier war load. Yes, the flanker airframe and engines can probably allow you to take 50% of that load out and still perform at the limit of human tolerance so you are not loosing much if any relevant agility, but then what happens if you recover from the first attack? Do you turn back and risk getting into dogfights, or do you punch it to get to 300km+ distance from the fight to re-commit at max range? At which point how much time have you really saved compared to just booking it straight for base and coming back with a fresh load of fuel and weapons and potentially even pilots?
On the other end of the spectrum, you are basically going up against a hopelessly outmatched opponent, so you can just sit back and just Turkey shoot them at your leisure. But just how many planes can you expect such a foe to put into the air for a straight fight against you?
While the advent of the drone spam era might have created a new niche for beast mode load-outs, it’s highly debatable just how combat and cost effective it would be to bring so many PL15s for such a role. I would think a PL10/TY90 beast mode load out would be far more appropriate for such a mission.