When someone is in a group, it usually means group effort and cooperation are required for the content.

If one person is not cooperating with the rest of the group, the group may find it more beneficial for everyone to kick this person. Seeing as the content requires a group (in other words, cooperation), someone who does not cooperate or adjust to match the play style of the party could become a hindrance.
If a healer is only healing, and not DPSing, and is not vote kicked, then the group must not find that person to be such a hinderance. But if they are kicked, then it is because they are not cooperating as a group.

Keep in mind, kicking someone requires a majority vote of the members.
With this in mind, a single person cannot kick someone from the group for not matching their playstyle. The group kicks someone from the group for not matching the group's playstyle. In other words, not cooperating or working together to accomplish a goal.

If someone wants to be part of a group, it is sometimes necessary to either:
A.) Find a group who wants to play similar to you.
B.) Adjust your playstyle to fit the group.

Otherwise, the first 50 floors of Deep Dungeon are soloable.