I think that the general trend of the advise here is pretty consistent: don't get too hung up on fly selection, worry more about finding aggressive fish, fish with confidence, etc. I would generally agree with all this, generally. I don't subscribe to the hard line "fly pattern doesn't matter at all" however. I do think that fly pattern *can* play a role in triggering an interest or strike, or spooking a fish, sometimes anyways. If you're fortunate enough to be able to fish for fresh, aggressive fish in optimal water conditions then pretty much anything goes; in other conditions I think it's wise to consider the challenges you're addressing to hopefully entice a potential player to grab.
Picking a giant intruder in times of low clear water, and skittish fish holed up probably would make a difference... it would likely spook a lot of fish. Of course, you never know, one of them might take an interest regardless and attack it... I would put a little time into putting yourself in the mindset of the fish that you're searching for, different day, different fish, different strategy. Water temp, color, pressure, etc all play a role in their temperment, even the kind of water can play a big factor imo. I will say that generally the more spooky, or vulnerable a fish may be feeling the smaller and more drab I tend to make my offerings. High water, low vis, cold temps, I usually go big, and flashy, with LOTS and LOTS of movement, and fish it slower and closer to shore. Of course if that doesn't work, I often try the opposite! Usually that works no better, but sometimes it does... maybe it was the different fly, or different presentation, or maybe it was just different.
I do think that something that looks, and behaves, like something that is alive tends to work better than something that does not. Of course my lack of confidence in "stale looking flies" limits how much time I've devoted to fishing them...
Problem with making any hard fast rules one way or another is that steelhead aren't quite that predictable. They have a tendency to do unexpected things, sometimes in unexpected places. Part of the mystery and the joy of chasing them is that there are few rules that need be strictly adhered to, and that there will always be surprises.
Do put some thought into what you're offering them, and how.
Do be certain in your selection, fish it with the utmost of confidence and be prepared for a grab at ANY time your fly is in the water and keep it there as much as possible.
Do try new things, and new waters.
Do pay attention to details.
Don't worry too much about any of this, and be sure to have a really good time with the process... the fish will come when they come, and it can be long time in between them. Or it could be the very next cast. Either way, it's a wonderful way to pass countless hours in beautiful places.