Super stiff suspension and lowering

Lowering links make the initial stroke of the shock stiffer. Try one and back the compression out a bit. If heights an issue then id say go for it. A lot of people get lowering links to work for them.

The best way to lower the bike is to have spacers put in the shock and forks, limiting how far they will extend. Of course this involves taking them apart, but just lowering one end of the bike will have negative effects on the bike's handling.

You said you messed with air pressures in the fork. So what have you tried?

Even though the forks are designed for a 450 and you have them on a 250f, given your weight i'd suggest starting with the stock recommended air pressure settings for the 16 KX450f:

Inner chamber : 165psi
Outer chamber : 14.5psi
Balance (bottom) chamber : 175 psi.

Make sure you are setting the pressure with the front wheel off the ground, and follow this procedure:
1. Let air out of the balance chamber
2. Let air out of the outer chamber
3. Set the inner chamber pressure
4. Set the outer chamber pressure
5. Set the balance chamber pressure.

If you feel that the initial part of the stroke is too stiff, try:
1. Lowering the outer chamber pressure 3-5 psi.
or
2. Raising the balance chamber pressure 5-10psi.

Also, dont forget that you have compression and rebound damping clickers on the left fork leg to use. Most people get too caught up on messing with air pressure and don't even touch the clickers. My suggestion is to start with the stock 16' KX450 air settings, and work with the compression and rebound clickers to get the feel you want. Start with the clickers in the middle of the range (12 out) and work from there, making 2 click adjustments at a time. If you still feel the fork is too stiff, then make slight air pressure adjustments to soften the initial part of the stroke up (add a few psi to balance chamber).

By the way. If you are thinking about getting rid of those air forks, please let me know. If they are in great shape i may be interested. Looking for a set to put on my KX125.

I have the same problem. I have a 15 kx450 and i cannot get the forks to move. Ive talked to alot of suspension companies and they all say you have to revalve. This doesn't make sense to me due to lack of movement in the first inch of travel. Has anyone tried playing with the shim stacks themselves?