Thrusting AND Slashing are both useful
It might "seem" slashing is more powerful because it involves bigger movements, and depending on the weapon, you feel, in your arm, that you're getting more force... but... it's not.
Thrusting concentrates more force onto a smaller point, allowing better penetration. Stabbing weapons tend to cause more lethal wounds (getting deeper to organs or major arteries). Thrusting tends to give less telegraphing and usually has better range.
On the other hand, stabbing attacks tend to have less short-terms stopping power - people often don't realize they've been stabbed, and can continue fighting back. For longer weapons, if your weapon is stuck in the opponent and they're fighting back, you can be in a bad situation.
Slashing tends to do more shallow wounds, BUT it's better at muscle damage which reduces your opponent's ability to fight back, and the force can move/maneuver the opponent's limbs or body into a position that allows you to follow up better.
This is the reason, around the world, throughout history, you can find a combination of thrusting and slashing weapons everywhere. There's usually only some periods where it goes particularly one way or another based on armor needs or conditions in which folks are fighting. (Heavy armor leads to a lot of thrusting weapons, folks having to convert farm implements, grain cutters or machetes get a lot of slashing implements).
Improving Thrusting Power
In this case, "power" means harm in such a way to debilitate quicker.
There's the classic piston-stabbing action, used with short knives and makeshift shivs - you keep stabbing the same area to try to turn it into hamburger. This is a common method in prison fighting.
"Twist the blade" is a term people use a lot, but depending on the blade's strength, the handle you have, and where/what you've stabbed, it may not really be feasible. "Jerk it around" seems to make more sense in actual situations - stick it in, jerk it around, to forcibly move the opponent and widen the wound channel. Again, this is going to be shorter blades, though the spear example would be to stick them then walk around or shove to pin them.
There are several locations which do much greater damage by targeting. Eyes and neck are pretty obvious examples for all weapons. Other organs also make a lot of sense, though the ribcage protects a lot of them requiring either good angling or heavier weapons to get past the bone.