Roster size is not the issue, the choices made for the spots are.
I think most people can agree that Jax/Sonya duo could sit this game out easily and give their slots to some other post MKT characters.
Kenshi's inclusion is questionable as well - Ermac already have telekinetic powers and with 3 variations will cover this magic type very well, Scorpion will cover sword attacks, so what exactly left for Kenshi? If they really needed more Special Forces characters (there like 5 of them without Kenshi already), why not go with Cyrax, who is more unique.
Anyway, the roster could be better, but it's ok and i will enjoy the game.
I'm sorry, but this is a silly argument. Most of the roster uses their fists and legs in their moveset, too, why not make an argument against the majority of them? A tremendous amount of characters use fire projectiles, based on your argument, only one should be included in the game. Kenshi's moveset and playing style has been shown to be very different than both Scorpion and Ermac. Characters who share elemental traits or powers have been proven to not be the same (Raiden/Rain, Liu Kang/Shang Tsung/Scorpion). Kenshi has not had his opportunity to shine in these games, is an extremely popular character and therefore, I feel like his spot is more than justified. Sonya, as much as I'm not a huge fan, survived the last game, and is one of the most iconic characters in the series ever. Her spot is more than justified (Also, the Cassie's moveset = Sonya + Johnny argument has already been proven to be false. She's very much her own character). As much as we'd like the roster to be 28 characters with three different and unique variations and each character being as unique as characters from Killer Instinct, it's not realistic. MK is right in the middle between KI (who takes months and months for each character) and SF (50% of the roster is aesthetically the same).
I'm one of the few that were disappointed by the dead characters being resurrected and being included in the roster (Jax, Kitana, Kung Lao, Sub-Zero, Liu Kang). However, it's not because they don't deserve it (subjective and a weak argument that should be ignored) or that their movesets are too similar to their descendants (which they aren't. The last to be seen is Jacqui and Jax, and given the amount of attention NRS has given each of these characters, I think they'll be just as fun to play). The argument should be that plenty of interesting characters through the MK series are being ignored when the plot could've easily justified their inclusion or that they're being killed-off pathetically in a comic. The dead characters being resurrected and included in the roster could/should have been saved for the end-game and those characters could've made a return in MK11 so others could have, finally, had some loving. Sadly, this isn't the route they wanted to take, and I still think the game looks incredible.
Lastly, the roster very much seems to be 25 + DLC (with Goro being DLC as the poster says. Not sure why people are arguing this). I'm not happy about the roster size because my expectation was higher, given what they said in interviews, but I'll have to deal with it.