Oh yeah, almost all content is soloable by RDM, with a few select exceptions. Even RDM/WHM, not so much due to new spells though, but mainly due to the level difference. 24 levels is a lot to gain, and brought a lot of new gear with it as well. Your magic accuracy will be nearly capped even with lower skills on most older content, while you get to have a large amount of refresh in your idle set. You also get access to Refresh II, which helps a bit, as well as Gravity II, even if it's not very different from Gravity.

However, /WHM does not offer much more than /SCH does, and /SCH has a lot of advantages. You may wanna consider that if you have it, or are willing to invest in leveling it.