Most active healing abilities don't heal to full health.
USF didn't either until they made the ambulance a toggle rather than an active ability. (Why did this happen btw? To cater to scrubs who couldn't micro it?)
Brit heal and ostheer medkits work the same way, they heal about 75-80% so if you're extremely low on hp you won't get quite to full health. Maybe there's some variance in the exact numbers but this has been my basic experience with such abilities.
I will respond to both of your questions, but find it sad you need to insult others just to ask a question.
1) Most healing abilities are designed to remove the need for the player to micro the unit while being healed. This takes time away from the point of the game which is combat and unit placement, not baby sitting base structures.
2) The ambulance was changed because it made no sense that a healing unit, often restricted to the base sectors, should require the USF players attention every 60 seconds to click a button. It would be like, rifles won't fire their guns unless you hit the "k" key every 60 seconds. It is needless micro.
The difference with Brit heal is quite large, it heals in a radius (so you can get multiple units healed simultaneously), it requires no cost after the initial investment. It is micro light, a single click gets it done. And it comes on multiple squads making full health healing easy. The only real similarity is that they are both carried by infantry units.