Garrus and Tali are from the ME1 squad, so yeah they don't really count. All the ME2 exclusives got shafted into cameo content, whilst 3 of the remaining ME1 cast returned as full squaddies alongside the continued presence of Garrus and Tali. So that's 5 of the 6 from ME1, whereas if you liked the ME2 squad you get 0, that's biased. Their cameo treatment was treated marginally better but with odd exception their actual content was poor and none of them got an entire DLC devoted to them as Liara did, so swings and roundabouts. Like you i wish they hadn't shoehorned in a bunch of new squadmates but equally even given that decision they should have had at least a single representative of the ME2 exclusives rather than jettisoning them all and hoping that by treating them all equally badly they'd avoid criticism.
If they don't "really count" as being ME2 members in ME3 because they're introduced in ME1 then even if the entire ME2 roster was in ME3 they shouldn't "really count" since they didn't originate in ME3. In that sense the only "real" squadmates ME3 has is James, EDI and Javik. Oh, wait, EDI was kinda in ME2 so maybe she shouldn't really count either.
So. ME3 only has two squadmates.
No, not "All the ME2 exclusives" got shafted into cameo content. Miranda, Thane, Legion, Mordin. All of those, if they're alive, are integral to the main story line. They're not just part of some random side mission you can avoid - which one can safely call "cameo" appearances. They're in the main, unskippable story. Again compare this to the treatment of ME1 squad in ME2 that could for the most part be ignored entirely or only exist for one scene for sake calling Shepard a traitor. Hell, at least your romances from ME2 get some attention. Not as much as they should, imo, but not as bad as what they did with our LI's from the first game in ME2. That was just dreadful, no matter how much Liara-haters would like you to believe otherwise.
I also disagree with the notion that they treat them all "equally badly". They've showed more "bias favoritism" towards the ME2 squad than they did the ME1 squad.
ME2 completely handwaved over half of your ME1 squad and all romance options. ME3 not only has side missions that include every single character (boy is there a lot of them in ME2) but SIX of them get special treatment. Garrus and Tali both there, can't miss them. Thane is there, saves the councilor. Wrex is there, big part of the genophage arc. Mordin is there, biggest part of the genophage arc. Legion is there, biggest part of the rannoch arc. Miranda is there for the start of the final Cerberus arc. That doesn't include the extra "optional" content they have.
Considering all these people could be dead we should be more impressed with just how much attention they actually received. It could had been so much worse... as ME2 taught us.
Being disappointed that your favorite ME2 squadies don't return to the gang in ME3 is understandable. Its a disappointment I share. That doesn't mean we should exaggerate the situation and stack the deck.
their cameo treatment was treated marginally better but with odd exception their actual content was poor and none of them got an entire DLC devoted to them as Liara did, so swings and roundabouts.
The Citadel completely obliterates the Shadow Broker dlc in terms of giving content to any one character. The SB dlc was not central focused on specifically Liara content. She played a role, certainly, but it was more on the SB story. The Citadel DLC for the most part exists solely for the sake of giving us more character interaction with all the characters with the story just being smacked on for the sake of saying it has one.