I would not agree, depending on your age and hearing, tone modification can make a huge difference in intelligibility.
Also, I find the P25 P2 sound on the Uniden radios very heavy in the low frequencies, crating a muddy sound hard to understand.
The 536 has a muddy deep voice not just on p2 but everything. I don't think other Uniden radios are like that.
A powered speaker is not needed to fix the sound on the 536, but an external speaker helps, because of the odd speaker tone in the 536 and because it's down firing.
In general, however, since the OP is talking about the hp2, which does not have this tone issue, a standard set of pc speakers, without bass and treble controls, works very well.
536/436/ws1095/996p2/996xt/325p2/396xt/psr800/396t/HP-1/HP-2 & others