Yes and no. Basically; if you want to be a pilot and you are qualified, then yes; you will be offered a UPT slot. The 500 is because believe it or not, at least half of the cadets don't want a flying slot. Some because they have other interests. Some because they want a FIVE AND DIVE. (Do their 5 years to pay back their obligation; then get out). But you are basically correct. If you are qualified and want to fly, you should have no problem getting a UPT slot.
Realize however that the word "QUALIFIED" is a loose term. In theory; if 1000 students graduate, and your class rank is #1000; you could still get a UPT slot. Will you? Hard to guarantee. Put it this way. If your ranking was in the top 500, you'd have a much better chance.
Also; realize that just because you got a UPT pilot slot doesn't mean you WILL become a pilot. There are some that fail out of flight school. There are some that wanted to be a pilot their whole life, but the first time they go in a plane, they puke their guts out and realize maybe they don't want it so bad. Or those that get into the altitude chamber and freak out. I don't know the wash out rate in UPT; but 100% don't graduate and become pilots. Some take other flying jobs. Some go into non flying jobs.
But if you are qualified; and you want to fly; you pretty much will be given a UPT slot. My previous post was to basically mention that there are 101 scenarios that make it where you don't get your #1 job.