There is no way the rear cinch should be tightened like the front cinch, creating 'even pressure'.
If a western saddle fits right, you can mount from the ground without the cinch.
My daughter once was cantering Trooper back up the trail toward me. I noticed something was odd. The I realized her cinch had come loose and was hanging 6-8" below Trooper's chest, banging against his front legs. Trooper being the little trooper he was named for, kept his pace without questioning. So I stopped her. She said, "Oh, drat!", dismounted, tightened and retied, then back up.
But she didn't need the cinch to hold the saddle on as they cantered.
And while I can't speak for anyone else, my cinch gets noticeably looser once I'm in the saddle. Apparently, my butt puts more pressure on the saddle than the cinch does. If I do my part, my weight keeps the pressure even. That isn't the cinch's job. IMHO.
The only saddle I've had slip came during a very hard spook & spin by Mia. (https://www.horseforum.com/horse-ridi...5/#post4940497
) The REASON it slipped was that it fit like this:
It ought to fit like this:
Folks who rope or run barrels or do exciting things I don't do may have a different requirement. For light trail riding, though...this is what keeps the rear of the saddle down:
BTW - the saddle in the bottom picture has a little too much "rock" - curve from front to back - to be optimum for the horse I'm using. But it is close enough for the riding I do.
BTW #2 - some folks just like having the rear cinch on. That is fine. I tried it and just felt it was extra 'stuff' for me to deal with - but no objections to those who like to use one. But you don't crank it tight to "balance the saddle".