No probs at all axel. Larger aircraft that can 'containerise' using ULDs in the lower hold, are less prone to pax distribution as the majority of the weight is spread out in the cargo hold over a larger area. Thus pax distribution is less of an issue. Most bags fit into a few ULDs. The rest of the space is filled with cargo containers. Think horse sperm to tomatoes to sports cars. There is far more revenue in the under floor, champagne free zone, than in the F/J cabins. Route/Flt/carrier depending. 737/a320s typically have 4 cargo zones to load bags in loose form, or containers for some 320s. loads spread evenly over a larger area underneath tend to reduce pax trim sensitivity.
As to the 707, it was probably easier to rotate with an aft trim limit. Handling for an EFATO (engine failure after take off) is better, in general terms, with a forward trim limit. Looking at old CFS notes from the RAF Little Risslington, the dart analogy is used. A dart in sport has all the weight loaded to the forward end of the implement. This aids it's stability through the air in 'free fall trajectory', yaw moments are more easily cancelled out with a longer moment arm from the rudder. Optimum CG is a balance between fuel burn/engine wear/safe handling(limited by regulation so not to be abused my MoL et al) and aircraft limits (usually super deeded by regulation). It varies by type, operator config, runways, weather, aviation authorities.