As previously explained, the player shouldn't be forced to play as Abby, it should be optional. Abby was boring and redundant, which ruined the pacing of the game. This is about as simple as I can explain my position. Hopefully it helps.
If you consider that finishing the game at Ellie theather sequence would have done it for you. Then you aren't obligated to play as Abby, consider that extra. And sorry but not only Abby gameplay is very different than Ellie the storyline is also very different with different purpose, only on the end it truly goes aligning with Ellie. But ok if you would be happy if they delivered only 30-40% of the game ok.
Yes, I think the game would be better if it stopped at Ellie in the theater. More isn't always better. In fact I think 'more' often hurts games as opposed to helping. As an example with FFVII Remake, instead of 24 side quests, 23 of which are horribly lame, it would have been better with 10 great side quests. Ghost is too long and really makes the repetitive aspects stand out. Dark Souls 2 has 'more' bosses than Souls 1. But Souls 1 is better because the bosses are better. I've never had a problem with short games, in fact I think short games are often the better, because the are focused and deliver well.
And we will have to agree to disagree. I thought the story of Abby was the same as Ellie. Ellie lost her father figure, sought revenge. Abby lost her father, sought revenge. The gameplay was virtually identical (minus slightly different weapons) and many of the levels were already visited by Ellie. It was just meh for me. I love playing as Ellie, lost interest with Abby. But had no choice to force myself to finish with Abby so I could beat the game. Feeling forced to finish something isn't a good feeling.