That's how they all turned into organized badasses.
That's a huge leap of a correlation. They were always organized badasses, even before the farm.
S3E1 literally starts off with a food raid, just like the other ones they've gone on. There's Rick, Carl, a pregnant Lori, T-Dog, Daryl, Glenn, Herschel, Maggie, and Beth. All they can whip us is a couple cans of dog food and a live bird. They can barely find enough food for everyone they have, let alone one more mouth to feed.
Right after that sequence, they have to leave the house because of an incoming herd. They all sneak out the back and get into cars. It's not too farfetched that they could've found cars during the winter.
They didn't all adapt over time, a lot of them died. During the group's time at the church, T-Dog died just getting into the prison, Lori died, Merle died, they found prisoners but they all died, they found Tyreese and Sasha but Karen and those other 2 guys died, a lot of people died from a sickness, Glenn almost died from a sickness, Herschel got beheaded, a whole army of people died during the prison invasion - Hell, even the fucking Governor died.
After the prison, 2 small children died. Also, which group would Dale be with that he would burden? Daryl+Beth became Team SuperMegaHuntingRunningEverywhere so Dale wouldn't have been able to keep up. Tyreese+Carol became Team PsychoDayCare so Dale would've been too much. Rick and Carl were...well, Rick and Carl so Dale wouldn't have fit in. There was Team GlennAbraham but that group was already huge. There was Team MaggieSashaBob which was another team based on running around and hunting. Also, I don't believe that Dale would have wanted to go to Terminus.
Also, yes. Judith is a baby. She has people carrying her, and feeding her. No one would be able to carry and feed Dale. Would you accept that Tyreese, one of Judith's caretakers, was weaker than Judith?
Between Terminus and now, a lot of people have died. One quote from the show has stuck with me. I forget who said it but someone said something along the lines of "everyone alive now is strong"
I truly don't believe that Dale had it in him to face the obstacles the group has faced between leaving the farm and now.