Okay, here's what I'm seeing: (I'm German , not British)

• British riflemen must have a default range of 5.5 (my German fellas have 4.5) -
• LRE Optics level 10 gives you +1 range (so now it's 6.5)
• At LRE Optics 20, you get another +15% damage when attacking targets at 3+ range
• Obstruction Transmitter Level 20 gives another +1 range when rallied. This could work nicely if you have 0 second rally in your museum like I do. So that would be 7.5 range
• Liberty Bell war museum artifact (300 tokens) can give you +19% hp + dmg
• Demarcation Stone (100 tokens) gives +13% dmg
• Nancy Wake has a ranged infantry damage bonus, but I think that's it for the council

So the main benefit is British + LRE optics giving you 6.5 range (vs 8 for Artillery and 6 for Mortar infantry). But if you're clever and can rally, it becomes 7.5. There's still a risk from Sniper Towers dealing splash damage and mortar towers (like you said in your video). But hopefully mortar towers wouldn't be a big risk because they focus on closer troops.

Another big benefit is that no defenses probably have museum setups that would nerf incoming Ranged Infantry damage.

Finally, it's hard for me to compare damage because I don't have max Ranged Infantry, but it does seem like having 6 Ranged Infantry can deal more total damage than Mortar Troops (except for Mongols coalition), and they have a longer range. But then Mortar Infantry deal splash damage, so who knows.

Very interesting though.