It seems like he could never provide for his family or afford their medical bills.

Landon certainly was. As his pancreas told him, sadly. :(

Pa was most certainly not a "loser" since he worked hard, was faithful to his family and rescued several people over the course of the show. I do wish they had Lars Hanson pass the mantle on to him as the manager of the millhouse when Lars died. Goodness knows he deserved it and that would have been an economic improvement for the Ingalls so they wouldn't have to talk about pinching pennies every other episode.