I liked the 1980s ACR
Fair call, remember I am a dinosaur who last played with APCs in the late 90s back when there was a Ready Reserve and we had an army of ones, I am, inspite of my efforts, more than a little out of date.
Looking at it from a whole of army point of view concentrating capabilities in specialist battalions and regiments and deploying tailored combined arms combat teams, battle groups and task forces makes sense.
I am very curious to see how the Armoured Cavalry Regiments evolve.
IMHO, the most interesting test case of what this stream is discussing, in the US Orbat anyway, was the ACR model of the early 80's, before Bradleys came into full use in Infantry units. The Cavalry units (i.e., the nominally dedicated armored reconnaissance units, as opposed to outright armored units) of the US army deployed maneuver units which were subdivided into elements of 4 tanks (originally M60s but quickly M1s), 2 AT vehicles (with M150s being the original kit before the M901 became available), 2 or 4 heavily armed M113s (.50 cal with shield instead of 7.62 without shield) carrying each a team of 5 dismounts. The element sometimes also had a SPM loaned from the maneuver unit for good measure (these tended to be M106s, so 107mm armed mortar carriers). The interesting thing happened when the M3 Bradleys arrived in Germany and units were able to cease operating the M150s or M901 side by side with the M113A3s as the Bradley accomplished both missions. The only major downside was the number of dismounts. Space for additional Tow rounds and a hefty amount of sighting kit was traded in and two of the dismounts were lost per vehicle. For the screening role of cavalry, 3 guys are enough to go set up an OP near a building or a forest clearing so as to allow the vehicles to remain out of IR and more importantly acoustic range. But they're not enough of a trip wire to know if you're stumbling on an enemy infantry force.
In Lebanon (Grapes of Wrath), the IDF used to assign an infantry squad to many tank platoons (essentially twelve tankers in three tanks to twelve guys in an APC). Since there were 9 dismounts, we're back to three per tank. So even if the US model for 'saturated' environments like flanks of the Fulda Gap were similar in ratios, the IDF issue in Lebanon was small ATGM teams sneaking a hit from a mile out at an M60, Shot or Merkava. They used the infantry as an additional trip wire for close security when the vehicles were immobilized at the top of a ridge providing overwatch for a column (a lot of THAT!) but they also doubled the pairs of eyes (the loader in a tank doesn't see much) to help spot ATGM teams in the distance. I remember an instance where a TV crew carrying a camera was spotted two miles out by an APC mounted infantry squad and killed by the tank crew they were covering at 3200 meters behind a brick wall they hid behind. At that distance, I guess they looked a lot like an ATGM team.
In 2006, IDF carried 3 or 4 dismounts in several tanks within two tank companies to bring along more of a reaction force into the ATGM saturated environment of SL. Contrary to a lot of reporting, I'm told the crews really benefited from the dismounts being available. In particular when damaged tanks needed to be evacuated without having another MBT lose part of its crew to handle the rescue.
I should say I respect everything that has been said here but I disagree about the benefits of 'pure' units. I think that's a lot of rear view mirror stuff. Combined arms at very microscopic levels is the way of the future. I see a very small maneuver force (as small as 500 men) divided into two assault units and one full size sapper unit. The way of the future is IED-like ordnance whether mines if a state actor or IEDs if non-state --either way, it will be outdated for commanders to expect speedy movement without much sapper support. In urban environments, they'll provide access through buildings to avoid front entries and to handle tunnels immediately. In other situation, they're a force multiplier to free the forward movement in the attack and to speed up the preparation of defensive obstacles in the defense.
Each Regiment can then have two armored assault batts and one 'pure infantry batt' to tailor the task forces. In the airmobile role, you'd still deploy two airmobile assault batts (including their own sappers) and one 'pure para or other infantry batt' for reinforcement or rapid reaction. Generally, US and IDF doctrine in movement are now quite differentiated but the USMC's current trend is, IMHO, very much trending to the IDF model of two parallel punches to essentially Thatch Weave their way forward. Best,