They should suck in unit vs unit battles, unless they aim at stationary units. The purpose of an artillery unit should be to force your opponent to move from a "save" distance away. I would guess their latest buff to range should make them okay for that. Try to mix them into your army and have an extra range that should allow you to "push" around your opponents army while staying out of range. Grenadiers are fast enough to work together with tanks. What is really bad for them is the first issue you mentioned. Grenadiers outrange that turret, but you can't easily use that because they walk into turret range by default.