I have had all ARC and/or Mc’s since about 1980 and feel like I’m familiar with the sound of the two manufacturers. Going through the list:
ARC D 52, VT 100 II, D 70 II . D 52 was dynamic, but smeared the highs with no imaging. Failed and blew up a pair of ProAc Studio 1s.
VT 100. Powerful and dynamic. Very detailed but thinned out the lower midrange to achieve this clarity.
D70 II. Best of the lot. Dynamic and “warm” but preserving great detail. I sold one but just bought another.
Mac MA 230 and MAC 1500, both rebuilt with the preamp section bypassed and acting as a basic amp. Quite dynamic, not slow at all. Punches above its weight. Have the 1500 now.
Mac 2105. A nice sound, powerful but not the last word in detail.
Mac 275 IV, pair in mono. Dynamic, warm, reasonably detailed.
Mac 275 VI. Detailed and powerful, but only after replacing stock tubes with 6550s, Sylvania AT 7’s, and real Telefunken ax 7’s.
Mac 452/462. Powerful, dynamic, quick and detailed. Great amps. Have the 462 now.
Mac MA 6900. Slow and heavy, the only Mac amp I just didn’t like. Now I use the 462 for movies and tv, and the 462 for bass and the D 70 for the mids and highs for music. The best sound I’ve ever had.
Sorry to be long winded, but broad brush assessments don’t tell the story. The sound varies from model to model. The most recent transistor Mac’s are the opposite of the 6900. They are detailed and dynamic, and not especially warm. The 462 is very neutral in its sound.The most recent ARCs reflect the house sound as to dynamics, as to other aspects of the sound I haven’t been able to hear them much.
Hope this helps.