Yep, but because this is the internet it gets changed to be because of Multiplayer because that is what some people want to use as the reason and then they complain that the developers don't talk to us when we don't listen when they do.
Since you can pause and select from all your abilities it doesn't make much sense. It could still have been there reason but if so it was poorly thought out unless they found some tie in between people who don't pause and not liking options.
It was probably a combination of things. They want fast action combat, for players who don't want to fiddle with radial menus while fighting (and lets face it, PC controls aren't on their radar), maybe because they thought more players would prefer this type of combat. This just happens to be good for multiplayer play too.
However when people say the game was designed around multiplayer, they aren't just talking about the combat style. The sp combat is literally multiplayer combat with double the abilities and pause. We have 4 characters but you can't control them as a group unless you use the added on tactical view. This is because the multiplayer combat the SP is based on had no need for multi character control. On the other hand, SP gets a new ability to revive fallen group members. This is because this ability was already there in the multiplayer system, so why take it out?
As for the 'official story' quip, that was a paraphrase of Joker in ME, as hopefully people realized, but it's true. They will spin any design decision publicly to look like it benefits the players, their customers. This is normal marketing practice. Companies rarely tell you the truth behind their design decisions. If a doughnut company shrinks its doughnut size, they say "This is better for the consumer because..." not "we want to cut costs, but still charge you the same amount for less product".
So, no, they aren't adding multiplayer so 'you can play with your friends'. They didn't limit abilities to 8 slots 'because it is more tactical and makes a better experience for players', and they didn't choose Frostbyte because 'it was the best engine, out of all they evaluated.
We can only make guesses about the real reasons they make their design decisions, they aren't likely to tell us.