Lots of times the one-click installs by the host have issues. They are often out of date installs and update on their time schedule not yours.
Doing it yourself takes a little more work but if you can follow a few step by step directions, it really isn't too bad.
Misconception #1 Bigger sites rank better. It is not so much that bigger sites rank better, it is mainly that they typically have more traffic because they essentially have more hooks in the water. IFF well structured and huge, it is possible to have them rank higher for a given search. There are some cases where a blog can help establish a site as an authority which will help a site rank higher for some searches, but it is not as easy as simply starting a blog. There are also cases where starting a blog contibutes negatively and does more harm than good.
Misconception #2 A blog with an offsite domain gets no benefit. There is some benefit in branding the two together for credibility and recognition. There is some minor benefit to having a growth in internal content, however, there is another benefit from having incoming links from an external domain. There is no blanket "one approach reaps all the rewards" when it comes to this. There are pros and cons to be considered, that just following a one method is best recommendation wipes out unecessarily.