I can not see the Arkansas Legislature as have much of a problem in passing the 14th Amendment. But then again, in 1865, 1/3 of these same legislature north and south voted against the passage of the 13th Amendment. The 14th Amendment may have been just one step too far beyond the line.
But if the states were "in rebellion" in not wishing to pass the 14th Amendment, and if the Congress passed such a bill, why didn't the federal army just go in and remove those legislators and replace them with someone who would? Were they afraid of something? Like maybe Geurilla warfare this time instead of organized armies in the field.
They were already running a "puppet" government in these states anyway. I don't see any evidence that they replaced anyone in Arkansas. They just denied these states their constitutional rights, as states, to participate in the governmental process. Which in a fair courtroom would probably overturn the 14th Amendment as being illegally ratified due to coerrsion of these states.
Getting 14th Amendment passed today may be more difficult than one would imagine. There is even today some discussion about what to do with, or maybe even repealling the 14th Amendment due to the illegal immigrant problem and their anchor babies. They may have felt that same way in 1867. This equal protection under the law may have been too much for these old boys to swallow even if they were loyal to the Union in granting that to the ex-slaves.
Remember Even U.S. Grant, when he was President, killed a Civil Rights bill in 1872, and one wasn't passed until 1964. Who said the UnCivil War ended in 1865?