You are literally better off spending those 3000 gems on the staple you want the most.
Chances are way higher and you don't get cut out from the box midway.
I wanted ninjitsu art. Now I would have been 60 packs in Electro Overload and possibly could build a XYZ deck in addition to transform.
Want Mirror Wall? Open Neo-Impact for additional Senju/Magician's Circle/Stamping Destruction.
Sphere Kuriboh? +Hane-Hane/Sonic Bird/Mask of the Accursed.
you spend 3000 gems on electric overload and its very likely you wont get trans.... you spend 3000 gems on the selection box and you very likely get at least 4 good UR's.
Selection box is obviously better unless you want one specific card
My UR drops
-Dark World Dealings (simply 🔥ing to me as a f2p)
-Senju (oh boy now i only need 5 more specific URs from 200 boxes)
-The weird red monarch dude UR whose effect didn't even motivate me to remeber his name.
SR drops for me were... well, forgetable.
Ye you are better off spending those 3000 gems elsewhere.
I got a Sonic Bird (^.^)/, the Ninja Trap, Kunai with Chain, Divine wrath and the Hamster Rat and some SR. I was VERY LUCKY because I didn't get a card which I already owned 3 off.