Could be game/engine specific; not all in-game limiters are worth using over external.
That, and I've just started the Yakuza series, and in Yakuza 0, I could only get the frametime performance to behave in that game by disabling game mode in the Windows 11 settings, so it's not always directly G-SYNC related.
As for there not being any frametime spikes in those instances, it's more accurate to say that G-SYNC automatically "reacts" to the given limiter's behavior, so if G-SYNC is lowering Hz, then it is an indicator that the frametime/rate rapidly changed during the event, whether the system-side graph reflected that particular instance or not; not everything is detectable with system-side monitoring, that's why many testing outlets use external monitoring methods for frametime performance.
Instead of being perplexed when you're experiencing frametime issues in a game, you should be more perplexed when you're not, since the former is far more common, as are game-specific quirks.
To be clear, G-SYNC doesn't really affect much of anything, and is instead much more vulnerable to being affected by everything else.
