I think both doctrines and practices of cults and abusive churches need to be considered because they influence one another. I noticed that abusive churches and cults of Christianity (Bible-based cults) usually have some specific set of doctrines which includes:
1) stress on the spiritual authority of the leader and the requirement to submit to him in everything;
2) the new revelation for this age given to the group leader;
3) the group as God's chosen people who have a special mission from God for this age;
4) other churches as being spiritually dead, degraded, or immature;
5) separation from other churches;
6) full consecration to the group;
7) salvation or God's reward is possible only for the group members;
8) leaving the group will cause losing salvation or God's punishment;
9) the leader's will is viewed as God's will;
10) work for the group is identified with work for God.
There are also some other doctrines.
Any group that has this set of doctrines is likely to be cultic and abusive. Doctrines and practices are interrelated. Sometimes, a church becomes cultic when they receive these doctrines, for example, when they read books that promote these doctrines. Sometimes, authoritarian leaders invent some of these teachings in order to justify their actions and twist the Bible in order to prove these teachings. So, it can be either way. Since there is a relation between doctrines and practices, both need to be considered.