So no one really knows what “Linear Arithmetic Synthesis” is. Roland never fully explains it, perhaps so it's specs couldn't be easily compared to competing digital synths. As far as the user is concerned all parameters are like a standard subtractive synth, but underneath I think the sound is being generated by putting sine waves together additively or maybe using FM. All the filter is doing is individually fading out harmonics as the LPF goes down. This also might be why the resulting wave is so quiet when the filter is all the way down because it actually continues fading out the fundamental instead of just stopping at a perfect sine wave.
On paper the D-10 (and others with the same sound engine such as the D-20, D-5, and D-110) and the D-50 seem very comparable. And actually, the MT-32, D-110, and D-550 all use the same tone generator (LA32 on all except pre-'88 D-550s that used a functionally identical older chip) and D/A converter (Burr Brown PCM54) on the output. But in sound there is no comparison. The difference is they are all implemented in greatly different ways. They all have different CPUs and program data, and they all have different analog output circuitry.
In my personal subjective opinion the D-50 is an excellent sounding synth. It is one of Roland's great pad machines capable of thick massive whooshing wall-of-sound pads. However, the interface is one of the worst synth interfaces of all time. You can understand it just fine if you put the time into it, but the tiered menu system creates a painful working situation of constantly backing in and out of menus just to adjust a few parameters. The whole process becomes extremely masochistic. If you have access to a software editor it's worth it, otherwise forget it. The D-10 with the cheap PG-10 programmer is a fairly workable situation. The sound quality is fairly poor though. It consistently sounds almost distorted with a metallic ring to all the sounds. I much prefer the Yamaha 4-Op FM synths, at least you can dress them up with processing to sound pretty good.