dozen photon torpedos won't penetrate the shielding of Ty'Gykor's
"The Ship" - a Jem'Hadar ship can weather an uncontrolled crash onto a planet - glowing brightly on re-entry - with virtually no damage in spite of an earlier inertial damper failure and the crash embedding the ship ninety meters into rock.
"Call to Arms" Weyoun: "Impossible. Federation shields have always proven useless against our weapons."
"In the Pale Moonlight" - Betazed's planetary defenses were obsolete and undermanned; the Jem'Hadar took ten hours to conquer the planet. "Strange Bedfellows" - if a Romulan planet's long-range sensors are out, that makes it an easier target. "Tacking Into the Wind" - Fifteen Vor'cha battlecruisers would barely scratch the planetary defenses of Sarpedion Five.
Jem'Hadar attack ships usually ram at ~1 km/s.
Jem'Hadar attack ship rams USS Odyssey at 285 m/s.