the XM734 was a proposal by FMC for an IFV based off a (modified) M113. basically it was a slightly bulked up M113 that had vision slits and firing ports added to the sides so the embarked troops could fight without leaving the vehicle, as well as an unmanned 20mm turret. it was a contemporary, chronologically speaking, with the BMP-1 development. this is apparently is where pentagon Wars got the idea that the Bradley started as a simple troop-taxi.
however that development program (MICV-65) instead chose to develop the rival XM701 proposal (by what is now Paccar), a heavier APC type vehicle based off the M-109 SPA chassis.
the XM701
this vehicle ultimately was dropped because it proved too heavy to transport by air using the C-141.
the modern M2 Bradley however traces its linage to the XM723, which was what FMC offered after the XM701 was dropped. it had been one of their alternate designs to the XM734. basically a light tank with a troop bay, it was substantially larget than the M113 based XM734. it used a (heavily modified) LTV-7 chassis, with a manned turret mounting the same 20mm cannon the MICV-65 specs called for. the turret had always been a requirement of the program, despite what pentagon Wars suggested.
the army then decided that the 20mm had too weak of performance against armored vehicles, and decided to upgrade to the 30mm bushmaster. creatign the XM2.
the recon role (despite what the film shows) was only tacked on towards the end of the development of the XM2, when the army realized the Xm2 could fulfil most of the roles of the XM800 scout vehicle program. (what was basically an armored car program) combining the two to use the XM2 chassis would save a bundle in the budget.
so the narrative that the film uses, that the M2 Bradley was a simple battle-taxi ruined by army hubris and bad decisions, is inaccurate. rather, it was a program that was always going to generate a large turret IFV, as that was what the Army wanted. the flaws in the M2 bradley derive mostly from the fact that the army basically wanted a light tank with a troop bay, but had to compromise due to weight and budget issues.