One C5 or one Rocket from any launcher only 20 Damage?

@JordanClick welcome to the "fun" gaming experience of the engineer class in 2042. By far the worst engineer experience of any BF game before it....

@JordanClick
The 3rd C5 was removed because Assaults should not be Engineers, and how dumb it was that Sundance can fly to the other end of the map and easily blow up a vehicle.
There is no vehicle to which C5 deals 20 damage if placed properly. There is no vehicle to which Lizzles do 20, RPGs can deal ~20 to the front of an MAV and M5s/SRAWs to the sides as well, and M5s/SRAWs can deal ~20 to the front of a tank. Either you had a very near miss, or you thought the MAV damage is the same for all vehicles. It's not.
You missed your rocket when firing at infantry. This is the same as BF4 (except now there's backblast from BF1/BFV, whichever introduced it). Rockets are not an anti-infantry weapon. Even then, there still is a pretty small splash radius in which they will 1shot infantry if you miss.
Grenade (and C5) throw distance is affected by your momentum. If you stand still, you will throw the grenade a shorter distance. If you're sprinting and jump, you will throw it farther.

@JordanClick For reference, some matches sometimes have faster projectile speed settings. In such cases, the projectile distance of the grenade will also increase significantly. (If you throw it as you normally would, you'll have trouble throwing it where you want it to go.)