I think Vulcan brains are fundamentally different in their ability to (almost) completely block out emotional reactions, but with those barriers lowered they have significantly more difficulty keeping themselves together than humans do. I am told that a human who tried to go “full Vulcan” with their emotions would mess themselves up pretty badly, but Vulcans manage a functional society of mostly decent people doing that.

Spock, therefore, would have found himself experiencing less overwhelming emotional urges than he experienced in his occasional moments of lost control, but with none of the vulcan-specific mental barriers he was accustomed to leaning on he had little choice but to roll with them anyway.

If those Vulcan mental barriers are variable in effectiveness between different individuals and different emotions, that would also present a needlessly technical explanation for why various Vulcan characters fall into obviously emotional patterns while maintaining very Vulcan outward behavior in other facets. Captain Solok and his racist vendeta as an obvious example.