It's the same instrument however many gradations of tom tom pitch you have-- not everybody sees having only two as a significant limitation. Or sees adding more of them as significantly adding creative possibilities. They're tom toms, they all have the same basic function. Tom stuff based on multiple pitches is kind of a narrow area of what you can do on the drums.
I agree, and would posit that the inverse is true also- not everybody sees having only two toms as a creative inspiration, nor sees adding more of them as an indication of lesser talent or unneccessary clutter/clatter.
I started on a 5 pc. with hats, 2 crashes, a splash, and a ride because I played rock (not of the hair band du jour at the time) & r&b mainly, and from school jazz band, learned that a 5 pc. didn't hinder playing jazz at all. As I learned to craft my parts in my first few original bands, I found that I sometimes- not always- wanted that number of voices in the kit, and that was enough to justify keeping the 5 pc. even though Nirvana, et al were making it uncool. Likewise, since I wasn't playing prog or thrash, I had no need for double bass or a bajillion more toms either. 35 years later, the kit hasn't grown much, and what little it has is from necessity, mainly after playing in cover bands for the last 20 years- china added for Stones (Watts played more china than people realize) and a few other rock covers that had it; splash stayed for Police and Pearl Jam and others; cowbell added for "Mississippi Queen", "Honky Tonk Woman" (there's the Stones again), and a few others; tambourine added for a couple of Petty tunes, "Let's Dance" from Bowie, and a few others; aux snare (the only drum I've added in all this time) for things like timbale (snares off) for reggae/ska and certain tunes with high-pitch snares like "Two Princes" and imitating short/high drum machine sounds like in the intro to one of the versions of "What I Got" and others. So far, I haven't had a sonic need to add anything else. I won't do it just to have more toys, but I'll add what I need, and if we play Police tunes that have more than one splash or a DMB/311 song that requires 5 more toms, I'll figure out a way to do it with what I have, 'cause I'm not adding gear for just 1 song.
Maybe I'd add an 8" tom if I'm ever tasked to do enough songs with higher pitch toms to justify it, but so far, 10/12/14 or 16 (12/13/16 early on) has it covered.
All that said, I've played a 4 pc. in a few situations that required the not-much-smaller footprint (saves more space at waist & elbow height, honestly), and I too enjoy the compactness.
You are creative or you're not. Taking down some toms isn't turning anyone into Weckl or Gadd
...neither of which are known for playing on 4 pc. kits, ironically.
Who said the pieces had to be toms?
Ultimately, no one, but I'm sure it refers to how the companies have traditionally offered kits in their catalogs- BD, SD, + however many toms.