The Cage (in which Spock smiles and laughs) was set prior to season 2 of Discovery (in which Spock is an emotional mess) which was in turn set prior to season 1 of Strange New Worlds.
You probably mean The Menagerie in which he effortlessly and stoicly steals the Enterprise to return Pike to Talos IV (under penalty of death, no less).
But those events are several years away, and it should not come as a surprise to anyone but the most devout of Voyager fans that characters should develop and change over time.
Spock is a dyslexic half human who also just lost his adoptive sister only about a year ago, in a very traumatic and very classified fashion at that. And on top of that, he, like Burnham, is still learning what it means to be human after a youth of being forced to be exclusively Vulcan.
It is logical to assume that one's ability to conquer one's emotions should improve with age and with experience (outside of Trellium-induced brain damage or plot-device geriatric diseases). He certainly seems a lot more in control now than when he was throwing a temper tantrum in Burnham's quarters (despite his setback in SNW s01).
The whole point is experiencing the journey that gets Spock to that point. It is no different than Cadet Uhura versus Lieutenant Uhura.
Isn't that what Trek is supposed to be about? The human[oid] condition?
Kbin. What you want is kbin.