First,

Your point on if a slave becomes prosperous as to be able to redeem himself contradicts your view of slaves being people who were under constant oppression as to never be able to own properties.

Secondly,
The bible actually mentions that slaves who prosper could redeem themselves. This confirms the point I have been enlightening you folks about that slaves were actually employees who could prosper and own properties.

Now there were two categories of slaves based on the type of contract they entered.

There were those eligible for redemption, based on the contract terms,

Then there were those who weren't, also based on the contract they consented to.

Those whose contract made inelligible for redemption were the ones known as bondservants.

So if there was any reason a slave couldn't be redeemed, it was cos of the contract type he chose.

Now I think the major issues you guys have are with these statements from Lev 26:
1. You can pass your slaves down to your children and they can be yours forever.

2. Don't do the same to your fellow Israelites.

Now, what's wrong with the first statement is the statement itself. It's a misconception.
The bulk of that chapter 26 was basically regulating on how purchase contracts are to made, and how purchases can be redeemed.

The actual form of statement 1 is " You may buy non Hebrews as bondservants "

Then the corresponding statement 2 is " Don't buy your fellow Hebrews as bondservants "

The reason for that was not preferential treatment as you suppose, it was stated as being because the Hebrews were already God's own slaves.

And just in case you haven't seen it, it is written in that same Lev 26, that if the Israelites saw a stranger or foreigner, they should provide and cater for them, not to make slaves of them as you guys suppose.