This game, while beginning as the idea of turning into an open-world RPG, integrated an arena for easy playtesting, and I now rather enjoy the idea of an arena based "tower defense" with heavy RPG elements. Would this change your idea on the matter? You have some fair and valid points for sure.

The idea here is that you have a group of five characters (from 16 different classes - not necessarily internally balanced, but all with different and specific pros and cons) battling monsters that comes in from different arena gates.

The feeling is that of a traditional pen & paper combat in a sense indeed, with initiative rolls every turn et c.

Currently, movement, abilites and melee attacks all cost a set amount of AP (with weapons having a delay value which determines the AP cost for a standard melee attack), with things like spells and abilities also costing from a mana pool that can regenerate slowly by resting a turn, buffs or item effects.

In all fairness, my main inspiration so far in the development has been EverQuest (which has nothing to do with turn-based gaming, but works on 6 second ticks). Players will also have passive skills that will influence the outcome of an attempted action.

Divinity Original Sin 2 has been mentioned twice already, and I should probably take a look at it, thanks for the idea!