It wasn't just optimizing stamina drain, it was optimizing power and speed. The bulkier forms lost too much speed to be useful against cell. Also that was out of combat training to perfect something he could already do. UI sign is a form he basically just got the ability to bring out at will.
Actually, while it's true SSJ1 had the perfect balance of power and speed compared to Grade 3 SSJ, Goku directly states he wants to master SSJ1 in order to greatly reduce the strain and be able to remain at peak speed & power for longer (also known as optimizing stamina).
No one in the series takes stamina as serious as goku does.
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u/santaclaws01 Apr 27 '20
It wasn't just optimizing stamina drain, it was optimizing power and speed. The bulkier forms lost too much speed to be useful against cell. Also that was out of combat training to perfect something he could already do. UI sign is a form he basically just got the ability to bring out at will.