I guess what you mean is that by them purchasing the "debt" they are - virtually- clearing the debt. Agreed in my opinion, however they will still mark your credit file.
All I have done with them is to tell them - in writting only- that I do not deal with debt collectors as I have never signed anything with them... eventually they'll sell the debt to another bunch of monkeys and the process starts again... after 6 years without recognising any debt or making any payment, the ccount will be "statuory barred" which means they cannot enforce anything in court...
Your credit score is back to his old glory then...

Nick