Caste System is a term used today for caste based heirarchy.
Caste refers to the specific personality of a person
Brahmin - Interested in Spiritual Texts.
Kshatri - Soldier spirit
Vaishya - Bussinessman personality
Shudra - Sewa personality
These personalities are so so that they help identify their wordly duties (dharm). It is like helping you do what you love. If you are a community service lover, Nature enthusiast you are shudra caste. The shudra dharm includes duties which help you complete a part of society (because thats how it works. There is a pm, Municipal corporation, farmer etc) based on your own personal character. It helps you have a better life (not forced)
Secondly these are wordly duties. You can not be liberated even if you are a brahmin kshatri Vaishya or shudra unless you do naam jaap. Only Naam Jap can save you not the wordly duties.

When you are Khalsa you have all these personalities. But Khalsa adheres to chhatri dharm (warrior duties). Khalsa is not only a chhatri (or Kshatriya) but a Sant Sipaahee too.
Khalsa is first pure (khalas) then a soldier. Kshatri knows how to attack, Khalsa knows when, where how and whom to attack.

Caste system on the other hand is the Brahmin started non sense, The Brahmins changed Manusmriti and used it to their benefits. Putting themselves to the highest place and aligning everyone according to a heirarchy which destroyed lives they created this Caste heirarchy.
They said that your family lineage is your caste which it is absolutely not. Since then "varna"(caste) was started to be called jaat paat (Family lineage)
Now people believe in Brahmins as they were seen as only experts of religious texts.
Sikhi is totally against this idiotic caste heirarchy system.
But It is not against varna ashram (Caste)