But by that logic if Strong arm increased your success rate from 98% to 99% that would be a 50% reduction in failure rate, but I doubt anyone would recommend taking it then.
Absolutely right, but perhaps you misunderstood me. I wasn't suggesting that my interpretation made a case on its own for taking SA, just that taking it can reduce the number of turnovers you get from throwing considerably. Whether that is of any use to you as a coach depends on a number of things, such as how many throws you tend to make, and whether you play your thrower on defence. As you rightly say, there are other skills which have more universal usefulness on a double and might be a higher priority to you as a coach.
As an example, my old OCC Orc team had two throwers, and I played them both (yes, both!) on offence. The higher level one (#1) had accurate, block, KO return and strong arm and the lower level one (#2) had accurate, block and safe throw. This meant that I could play with #1 in the backfield on his own on offence and he could get the ball from just about anywhere from the kick. On turn one of my drive I could cage up pretty on the centre of the LOS (usually at least a square in after LOS blocks with a troll and 2 BOBs) with #2 in the cage and use #1 to pass the ball to him from anywhere in my half with good odds of it working. Starting an Orc drive on the LOS with the ball gives you at least a turn extra to score as you're not transporting it upfield on foot, so this tactic helped my drives a lot and was very useful against fast agile teams who tend to flood the backfield (skaven/elves).
So what? Well, since this was a setup play which dictated the drive for me, reliability was key. Minimising turnovers mattered here as it meant that I could set myself up for the drive more effectively - my "line" pretty much had to retain shape until the pass was done to try to keep the backfield covered, but once the pass was done then I would want to make other moves in order to improve my field position (important for a low MA team), and that's what reliability allowed me to do.
Would other stuff have been more useful on that double? I had 9 players with guard and plenty of MB too, so that wasn't needed. Nobody else had dodge, and I didn't want to commit to taking it on lots of players, and I saw little use for SS on a player who, ideally, won't be getting blocked. Having a credible passing game on an AG3 teams is also a bit of a gamechanger - it adds a dimension to your attack. As such, SA seemed like a good bet in that case taking all other considerations into account.
So yes, consider all things, including how often you pass and how well you can deal with turnovers from those passes and whether reducing that would be of benefit.