

The Alegebraliens being in TPOT is not a problem, but the fact that they're not treated as individuals is
So the show started with Four and X as the main two Algebraliens, then Two was added in BFB 16 and hosted TPOT for a while before then One was properly added in TPOT 12. There was also Six added later in an episode I forgot. Seems simple so far. While this was happening Jacknjellify made subscriber specials involving the Algebraliens larger than Four. (surprisingly the ones less than Four were never shown until Two in 2763K and One and Three have never been seen in a sub special)
Throughout the season there have been hints of the other Algebraliens existing, but nothing too crazy. Even TPOT 15 had direct cameos as hosts and that was still fine, just a little nod.
Then TPOT 20 came and the Algebraliens were all just one unit. I mean, in the sense that they were a coalescence and not their individual personalities.
What do I mean? We all know Four as the sadistic host who blasts contestants at a moment's notice, (well at least until Post Split tampered with that a bit...) X is the kind and cute host who's besties with Four, Two is also a kind but charismatic host who gets along with the contestants well, and One is the shifty villain who gets the contestants to sign her deals to get her way, and of course is really power hungry.
To be honest, the rest don't do much as individuals. Let's take Six, the one Algebralien still adventuring through the equation playground. Why them? What makes Six inherently the one to explore the halls of Four's internal dungeon? Or could it be any other character?
For Three... y'all need to hear this because nobody else is saying it. The most significant contribution to the plot she had is that she died. That's it. Why Three? It was probably because they happened to be the last single digit Algebralien introduced to the plot, Two and all the Algebraliens Four and above got introduced while One was introduced later while Three was the last. Like I could see any almost any other Algebralien taking her place as "One's friend who dies".
With Five, Seven, Eight, Nine, and Ten, I don't even know what they're up to. Might as well just have one of them because in TPOT they're five of the same character meant to represent the whole being the Algebraliens.
The five Zeroes and Fifteen. Yeah. Zero put it best when he said that their lives had no meaning after Fifteen died. Their lives never had meaning to begin with.
I'm not saying give each Algebralien a major plotline like Four, X, Two, and One. But at least give them their personalities man. Otherwise they're only seen as plot devices which is doing their character a disservice. I know their personalities were only established in sub specials which aren't canon but then why should we expect them to be in TPOT? Do we need the five Algebraliens with Balloony and Announcer when one could've gotten the job done?