It is just a misinterpretation...that most people dont quite understand...before you jump on me, again it is just my opinion...LOL
It is the same when people hear of the word, distortion, in audio. Most if not all will right away think of it as a negative interpretation.
Audio or sound engineer will say otherwise, not all distortions are bad. In fact, what we hear from a typical tube that is described as tubey, airy, etc...is a form of distortion.
Back to the word, aggressive...yeah, I cant think of a better word to describe it. IMO, I still think it is a simple and direct word to describe the sound signature of most TS tubes compared to say, the typical British sound from most British tubes. Tubes with aggressive sound signature do not necessary mean they sound bad. To me, it is generally referring to fast, dynamic, high clarity, heavy bass, etc...you get my point. Personally, I would prefer to use these tubes for fast and bass heavy music genre like heavy metal, rock, electronic, etc...You wouldnt want to use a tube with slow and extremely euphonic tone, would you? In other words, aggressive sounding tube can be good.
Yeah, I listen to a wide range of music genre from pop, heavy metal, rock, jazz, blues, folk, instrumental, classical, J-pop, K-pop (not that I understand what they are singing...LOL), anime, C-pop, etc...
P.S. the echo you describe is actually not echo but what sound engineer called harmonic distortion.