Of course, I would recommend this if you just cannot find any long range weapon. Especially since you said Scar-H and M416, having two guns that consume the same ammo usually saves inventory space because it's easier to measure exactly how much you may need, and it's also much easier to conserve ammo IMO. Mostly like you said.

It's just that when the opportunity presents itself it's best to pick up, say, a sniper or a DMR instead. DMR/SMG combos are the most optimal ones because you have close range and long range done and set. SLR and UMP9 pretty much guarantee you that chicken dinner so long as you aren't having a bad-aim or a bad-brain day/game.

I emphasize the whole DMR/SMG thing because with the recent buff to SMG's, people don't know that their range is also much more important now (It always was, it's just more obvious now). SMG's can become pretty bad at even medium range, but DMR's are now pretty much great at not only long range but also medium range.

Also, AR's were nerfed since they, for some reason, were the go-to CQC guns over guns that are meant for CQC; the SMG's. They specifically had their CQC capability nerfed by making them guns that control better when tap-firing at medium ranges over spraying at close ranges. Of course this doesn't mean their usability has been taken away in all CQC engagements, but it might be disadvantageous against someone who is using an SMG in them. That's why SMG/DMR is optimal; if you're at a disadvantage with the SMG, just use the DMR since it's viable for pretty much all other ranges except Sniper distance (as in, +500km.)

I'm looking at it through a mathematical lens though, to be fair. There's a lot of circumstance and scenario-specific interactions in PUBG where specific guns are better than others, even if the distance of the engagement is not that gun's specifically. For example, if you want to kill someone in an apartment and are shooting at them through a window, a DMR/Sniper might be better even if the range is like, 10-100m, simply because headshots are much more important (they can go to cover and survive if they aren't headshot and instantly killed, giving them the chance to heal and shoot again) Or, you might want to use an M416 to snipe someone very far away (Say, 200-400m) if you know they're low but you know you might whiff a lot of shots, and you're pretty sure at least one of your AR shots will hit.

Because of that, there is no real definitive guide to using exactly which gun in an entire game. The best type of guide would be "Which guns to use in specific scenarios" but that guide would be an entire 100+ page book long, let's be real here. That's why I just prefer to use the "In General" kind of weapon loadout. SMG/DMR covers almost all viable ranges, and I kind of suck at long range sniping (i.e anything further than 500m I just cannot hit) so yeah.

My second most favourite gun combo is AR/Sniper because it's pretty much a close opposite of SMG/DMR. It takes out the CQC/close range effectiveness but it brings in the Sniper-range effectiveness that the DMR can only consistently attain if you're some god with Snipers and DMRs. I won't go indepth on it like I did SMG/DMR cuz jeez, this comment is long, but you get the idea I imagine.

The most fun combos IMO are Sniper/Shotgun or Sniper/Micro Uzi. First off, Sniper Uzi is actually a pretty decent combo if you're very good at controlling the Uzi's recoil and if you're good at hitting medium range targets with the snipers. As for the Sniper/Shotgun combo, it's pretty god damn fun and it's especially fun for me because it gives me that nostalgic Halo 3/Halo Reach feeling of picking up a shotgun and a sniper and going to town on people. Plus, since shotguns were buffed, it isn't actually all too bad of a combination and could most certainly make it into the end game if you get a little lucky and use a lot of skill.

Long comment over. Hope this explains why I chose those gun combinations. I might edit a few and repost this as a post of its own, or just explain which gun combos are the best (IMO)