I'm a mage yeah, and I agre with what you said about it being a market trend for action rpgs, but that trend primarily exists due to consoles, that the majority of triple A games are making the most money out of console games and so the style of play dedicated to it it indeed console related.
If that if they had truly gone for an action game they would have found a way to limit the number of active to fit the number of slots. Since console versions of DAO and DA2 had no such limits there is no ground to put the blame for this limitations on consoles.
As mindboggingly as it may seem, I'm starting to think that just like they thought that scanning was fun in ME2, eavesdropping quest were immersing in ME3, or repeted environnments in DA2 had artistic value, it's very possible that they really believed that limiting the number of available actives was both elegant (beautiful symmetry on the screen ) and tactic (as in frustrating).
This is not the first Bioware gameplay decisions that makes no sense to me. These are the guys that brought back no auto attack despite the uproar it caused in DA2 (with both PC and console players).
As unfortunate as it is, this game has problems because people at Bioware made poor decisions. The existence of consoles and the eventual market skew toward consoles is not a valid excuse for a company developping PC games for twenty years to suddendly forget how to make a PC UI.
This does not explain the 8 ability slot limit, the absence of a chest, the reduction of companion tactics, the MMO style side quests, etc. All unfun on all platforms.
For the record I game on PC since I bought Dark Forces and Warcraft 2 in the mid nineties and I bought my first console to play Mass Effect at launch almost eight years ago. i have enough experience playing on both to see when something is a problem on one or both machines.