And my responses:

1) Short barrels have substantially inferior velocity and will experience more drift and require more arc at a given longer range. Additionally, 5.56 from a short barrel loses its terminal ballistic efficacy very quickly. It'll punch small holes much farther of course, but I would not choose to take a 10" AR to a 300-yard gunfight. That's why I consider 10" and below ARs to really be sub-150yd guns. And at that range I don't need them to be any better than minute-of-chest-cavity.

2) Yeah and then get a shit-ton of glare and reflections, and it's still nothing like shooting with a 6.5MOA dot.

No2 First. Yea, you can have a 6.5MOA dot obscuring the target or you can have the bloom from the glare obscuring the target. However, the 6.5MOA dot obscures the target all of the time whereas you can turn the 2MOA brightness down if you wish.

No1. You may not have the choice of which weapon is in your hand when you have that gunfight, whether it is at ranges best measured in feet or best measured in yards.

Bullet drop and windage issues are real, but not so substantial as you make out, and drop is easily recalled for hold over. Using Federal's Fushion MSR ammo, for example, out of a 16" barrel velocity at muzzle is 2750fps, at 300yds it is 1942fps, drop, using a 50yds zero, is 10" and wind drift @ 10mph is 10.9". Taking muzzle velocity down to 2450 to represent shooting it out of a 10.5" barrel and 300yd velocity is 1699fps, drop is 16.5" and wind drift is 13.1". The 62gr Fushion bullet still opens at that velocity. You can run the ballistics at different ranges and velocities using the Federal Ammunition on line ballistic program, found on the Federal home page.

The first video down shows the 62gr Fushion performance in ballistic jell at 1703fps. https://homedefensegun.net/fusion-ammo/

Also, here on AR15.com is a bullet test of M855A1 ammo at reduced velocities to test bullet performance at range out of an SBR: https://www.ar15.com/forums/ar-15/The-Army-s-New-Ammo-Is-a-Long-Distance-Devastator-M855A1-Gel-Test/16-724711/

There are other 223/5.56 bullets which will perform adequately at 300yds as well.

6.5MOA at 300yds is more than 19.5". 19.5" is greater than the width of a human chest cavity. However, I would suggest that any hit at 300yds is going to be a win, whether it is chest cavity, guts or or peripheral. 19.5" is still greater than the width of most humans, and much greater than the depth of a human torso.

Perhaps you might find a 4MOA dot a good compromise. 4MOA is just a bit more than 12" at 300yds and the dot would obscure a torso, but not the whole width of a human.

JPK

Switched over from an Aimpoint CompM2 to a Leupold VX3 1.5-5x on January 1st of this year to test out the LPVO concept on an SBR. Optic had previously been on a very heavy SPRish rifle that hasn't seen much use lately, but that I have previously put to good use in a few Urban Precision Rifle courses.

So far, I am liking it quite a bit. It is a fairly old scope, and the illumination is not bright enough for daytime use like a lot of the modern 3-gun oriented offerings, but the duplex reticle is actually really fast, even without that feature. Eye box is slightly less forgiving than an Aimpoint, but I have so far not found it to be a major hindrance running VTAC Barricade drills and the like.

I don't know that it's the answer for everyone, but in a role where  a high degree of precision might be required at 100-200 yards, or where magnification could be useful for surveillance / target ID, I think the concept has some merit.

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I use a TA31 RCO on my 12" SBR. It's a badass rifle, heavy but solid performance.

I'm interested in the TA44/45 1.5x small package concept and am curious how the eye relief could affect my shooting. Do want to try it out & believe I could be inclined to it over an MRDS.

I wear an eye prescription and so red dots don't always agree.
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Currently use the PA micro it works for me set up on a 9" Blackout.

Primary arms 2.5 acss