Actually, having a cassette max out at 30t is bizarrely high for a gravel bike especially if running a 46t chainring. Unless 30 refers to the inner chainring on a 2x, in which case it's lower and therefore easier than road gearing so definitely not a reason you can't keep up.
That segment you linked to is long enough that you need to work on your sustained power. Sweetspot or threshold intervals are simple and effective. If you had a powermeter, it would show how little power you're actually putting out on the flats and how much more is necessary climbing, which would help demonstrate how a lot of your current riding time might not be conducive to getting faster. You can use your imagination, but real data is generally more eye-opening.