It's hard to understate how important the specific year/spec the speakers are is when talking about this. Other stuff matters of course like cab construction and such but just for a thought experiment here:
2020 Marshall 1987x + 2020 Marshall 1960AV (4x V30) cab
vs
2020 Marshall 1987x + 1990 Marshall V30 cab
Those are going to sound extremely different, even though at face value it looks very similar. To matters worse, "V30" encompasses quite a few variations in spec. I'm not an expert on all of the different ones but my '96 Fender Tonemaster V30's sound noticeably different from my '03 Mesa V30's which sound very different from my 2012 V30's. Even if I put them all through the same cab - very different sounding. So the wrong combination of specific type and year of V30, plus different cab construction means that a bright amp like a 1987x might emphasize unpleasant frequencies.
Why I’m not a fan of those g12t75s—too scooped.
Another example here that I know a little it more about. I hear this all the time but it's yet another spec difference. I have an '86 Marshall cab with '86 G12T75's with the old logo and vents on the back. They are dark, thick, low mid-heavy speakers - not at all scooped by any stretch of imagination. In contrast, I have some 2014 G12T75's which are much brighter and therefore scooped sounding. This isn't a difference between speaker break in either, although that can be a factor. The specifications changed.
So while we "normal" people just get the friendly names - V30, T75, Redback, Greenback, etc - there are changes in cone construction, glue, voice coils, and other stuff behind the scenes that your average player doesn't necessarily know about. It's certainly not as "cool" to talk about but check out this list of different G12T75's I lifted from another site:
T3478 G12T-75 Ceramic 8 Ohm cone stamp - 444
T3781 G12T-75 Ceramic 8 Ohm 75w, 85Hz, 97dB, 1.75" coil, cone stamp - 1777
T3760 G12T-75 Ceramic 16 Ohm 75w, 85Hz, 97dB, 1.75" coil, cone stamp - 1777
T3880 G12T-75 Ceramic 16 Ohm Smooth cone. Cone stamp 6559.
T3947 G12T-75 Ceramic 16 Ohm cone stamp - 444
T4573 G12T-75 Ceramic 16 Ohm Orange. 75w. 1777 cone.
That's 4 different construction codes just for 16 ohm G12T75's, two of them with completely different cones. So you may try some "T4573" T75's and think they sound like crap. But "T3880" is going to sound so different you may as well not even call it a T75 anymore. And this is just what we know of online, for all we know there could be 20 different specifications tied to the "T75" name.
It's better to think of stuff like V30 or T75 as a series which contains multiple types. In the same way the Type R, Si, EX-L, EX, and LX are all "Honda Civics," someone who has only driven a Type R might think all Civics are track beasts. But online you wouldn't recommend a Type R to someone in the same breath as an LX Civic because they are very different cars for different purposes. Not a perfect example but I think it illustrates my point.
My 80s era T75's sound closer to my modern G12-65 than a modern T75. I was extremely wary of buying that cab because I kept reading about how scooped and crappy T75's were, but I took the risk, got it home and started playing and was really confused by how dark they were actually, at first I thought something was wrong with the cab. It ended up being a pleasant surprise because I was looking for a more vintage classic rock sound and the cab nails it.
