I think it really doesn't matter. Zooming in too far and getting too technical. For me it's about product placement and where I want their skill sets placed for their role in a particular defensive play. Think of it this way. 1 formation: Goal-line. Basically all LBs pass rush and bring the house. Dime - only MLB is present and it'll either be coverage or a blitz but neither the WLB or SLB is present. That's 3 formations where zooming in super deep doesn't matter leaving Normal Defensive Set and Nickel Defensive Set. Nickel lacks the SLB so now you're only stocking a MLB and WLB in this formation.

It appears to me that the SLB is on the other side of the line from the TE and would be present in 2-1-2 runs such as HB Blast and rushes in that direction. SLB is also the LB more apt to be nosed right up on the line in a defensive play.

Personally, I think it's about honing in on your Normal Defensive Plays and 1 by 1 deciding which LB plays the best role for that play and the formation within the Normal Defensive Set.

Edit: I'm wrong. SLB is on the TE side, therefore, some plays he'll cover the TE and also pass rush and cover runs going in that direction.

all of this is very easy to see in the depth chart/overides tab. Be sure the sets are cleared, and at you main depth chart has one named player at each position (Ifor clarity: a WLB at the WLB, RT at the RT column, MLB at top of MLB column, SLB at top of its designated column.
Then the overrides chart will show exactly where they line up.
Keep in mind if you have a SLB at the top of the MLB depth chart column, that SLB player will show in the MLB position in the override tab.
I don't have the moment right this moment, but if anyone wants me to kick some reference pics I can do that later.
It's too early to be as clear as I'd hoped to be lol.

this is why I like to treat all three of my linebackers largely interchangeably - all faster guys who can do man coverage well (I'm not a huge fan of zones) and who can tackle. If they can rush, I generally put them at one of the outside spots, since I like to throw in blitzes.

By doing it like this, I don't have to worry about making sure the right guy is on the right side

Can he get A R'amen from the crowd?!?!
R'amen!
Spaghetallelujah!!

From my Observations: in 4-3 you essentially have a R and L LB rather than strong and weak , they mostly have the same job. In 3-4 the slb is part of the base 4 man pass rush(not all plays) (but seems to be very ineffective in that role from my observations). The Alignment of your LB isnt really all that important , since the play usually tells you who is responsible to cover who (aka who has receiver 3,4 and 5) and zones are really only a gamble on your player standing in the way effectively

it is a huge difference if the WLB or the SLB has to cover a 198 lbs WR playing RB instead of a 263 lbs TE.

A lot of blitzes have the mlb and the slb covering the third option . When it’s the slot is a clear mismatch. My 256 pound guy gets torched routinely. Good or bad overriding a smaller faster guy there is key. Creating a big nickel out of a 4-3 or 3-4 . Or some version of a big dime set out of the nickel here.

For me our alignment issue hurt the pass game a bit but run fits are destroyed. Huge gaps on plays where there should not be. Making certain plays a lot better or worse when they face other certain plays. This only due to presnap alignments .

Here I will blitz to keep that gap and integrity....or steer clear of nickel all together . Same for passing scenarios there are plenty where guys are just uncovered. When in reality it just wouldn’t work that way to the level it does here.

Strong side is not defined by the TE only. It is determined by the amount of players on the line of scrimmage to that side of the ball. You can have TE left and still have strong side right with 2 WR on the LOS. I didn’t take the time to look at the play in question but TE does not determine strong side or weak.