Is there something wrong or missing with Construct's built in platform movement?
The platform movement is miles better than MMF's default platform movement, but it still has problems.
1. Holding Jump down makes your character bounce around like he's on a pogo stick (should be a checkable option to be able to turn it off).
2. Holding both Left and Right at the same time makes your character walk funny (the movement favors the last control you press, so you character sometimes walks backwards). With both keys down they should cancel each other out which means the player would stop horizontal movement and stay facing the same direction he was going. This can be fixed by adding a series of events to correct it, but even so it's a flaw.
3. Lack of customization at runtime for gravity, jump strength, jump sustain, and speed.
If you could manually manipulate speed, you could create things like horizontal moving platforms that add their speed value to the player's speed, or conveyor belts, or enemies and npc's that use platform movement, or ladders and ropes to climb (by manipulating y speed) etc.
If you could change jump strength and gravity you could create springboards to launch the player in the air, swimming areas, low-g sections, etc.
To a lot of this stuff with the platform movement as it is now means having to manually update the player's x/y coordinates, which means you lose the benefit of the platform movement's collision detection. And if you have to start writing new collision routines to compensate for that you're basically making a custom platform movement anyway, so the default one loses it's usefulness for anything but the most basic stuff.