Wrong.
They are just different.
MiG-27 was supersonic fighter/bomber (light tactical bomber in fact) while Su-25 is dedicated subsonic armored CAS striker.
A military trainings report from Kant VKS AB in Kyrgyzia:
http://www.vb.kg/doc/343351_na_rossiyskoy_aviacionnoy_baze_odkb_kant_proshli_letno_takticheskie_ycheniia.html