As noted, your HF rig attenuates MW so help with front-end overload from nearby commercial broadcasters, especially for 160m band reception, as that amateur band is right above the MW broadcast band. If operating at 160m, you ideally want to hear other amateurs instead of splatter from nearby AM broadcasters.
The reason the A99 sounds "better" (probably more like less noise, right?) at MW is because of its dramatically compromised efficiency at such low frequencies.
Your A99 has a significant matching section, as it is basically a 1/2-wave, end-fed vertical dipole for upper-HF. Forget a tuner, too, IMO. In a pinch, the A99 can go down to the 15m amateur band with reduced efficiency via a decent antenna tuner, but it really drops off below there. It is a decent antenna for 11m CB, plus even the 10m and 12m amateur bands with a quick adjustment of the antenna's tuning rings. It is way out of tuning for MW, or to be straightforward, actually for pretty much any frequency below the 12m amateur band.
About the "random" wire, there are numerous variables involved in the performance: resonance, impedance, RFI ingress, etc. Noise can be an issue with simpl longwire antennas, especially due to common-mode coupling from the feedline. A 9:1 balun (or other ratio depending upon wire length) could help with noise, plus improve impedance matching.
Being realistic, any seriously widebanded HF antenna typically is a compromise, again for numerous variables. If you are looking for an off-the-shelf MW/HF receiving solution with a moderate footprint and a simple end-point feed, consider taking a look at the basic Par EF-SWL. That said, a balanced antenna, like a fan dipole (for your bands of interest) or a large horizontal loop would be even better IMO. A good start for more antenna ideas, and even more so if you do not mind building your own wire antennas:
http://www.hamuniverse.com/antennas.html
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