The perspective of an op who has used CW 95% of my last 49 years as a ham, and QRP 90% at that. I know how to be heard- and I know how to pick out an op in the mess. Verbalizing my thoughts isn't so easy.
As 'JT' pointed out, you cannot form a 'long T' with an Iambic keyer. But I say it's simply not needed: any T will accomplish the same, and after 49 years of copying them, believe me, when I hear a 'T' where a '0' should be, my brain does the correct replacement instantly. I hear a '0', not a 'T', and it doesn't matter the length of the 'T'.
'WPM' - When there is a mash, all exactly on the same frequency, all calling at once... there are several things that distinguish you guys in my brain:
1) Cadence and weighting. Even if every station used 'perfect' (it's actually awful) weighting of 3:1, your timing is all different. And believe me, I can hear it.
2) Timing. Timing is key. I don't care what form of input you use- your timing is about as unique as your face. I don't mean the timing you use when making your call, I mean your inter-character timing. And it doesn't matter whether you're using grand dad's J-38, your pretty new Begali, your junk MFJ-564 (see my youtube video for magnetic tension mod) or your homebrew paddles. They're now positive, snappy and crisp). Maybe if you're using a keyboard keyer you'll sound the same- but even then, in a rag chew, you'll start to stand out because you keep letting the buffer run out then you're reverting to hunt-and-peck typing and you'll start to sound unique, but this applies to sounding different in a longer QSO, not in a calling pileup.
3) As an aside, many hams who run a linear amp sound different due to amplifier variances in distortion products, TR switchover, etc. And if a ham is using an older vacuum tube transmitter with cathode keying and a straight key, I'll hear the scratchiness in his contacts. Very few sound the same. But this applies mostly to 1950s thru 1970s ham radio. Haha. Modern solid state rigs pretty much sound the same to me. I cannot state strongly enough the shocking processing power of your brain when it comes to figuring out the world around you.
I have a completely sightless relative. He drives his truck into town. How? By the sound of his tires reflecting off of the gravel country roads. It's true. He shouldn't, but he does. I'll bet you a sightless ham can separate those signals, all on the exact same frequency. Easily. And not be able to explain how.
Regarding being 'exactly on the same frequency':
It's amazing how many rigs these days are actually very close to being on the exact same frequencies, to the tenth of a hertz. Yet most are not after they've 'been in the field' for a few years and have aged. I can easily detect a difference between two stations that are less than one Hz apart. After 49 years at copying CW, you'd expect this. I can also carry on two concurrent QSOs- one with the op on the other end, in CW, and one vocally with my family in the room. You'll gain this ability too if you do it enough. You can read a book and chat with your wife or kids at the same time, right?
And oh man, if you want to be heard? DO NOT transmit on the 'same exact frequency' when trying to be heard! To do so is an exercise in masochism. I'm a life-long QRPer. I learned how to be heard

There is no finer way of standing out. And it doesn't have to be by much- 20 or 30 Hz works a treat, even when running SSB. Heck, especially then

Just my two cents worth.
I've done quite a few videos for new CW ops, offering my hints and experiences, if anyone cares to look. Channel not monetized, My CW playlist is at:
https://www.youtube.com/playlist?list=PL3CPduOS04Nck7TqKaLq7zbyrV1R9gioaChuck, N8NK