The text files are millions of rows with 50 columns
Small. Why an SSIS package?
They don't open in notepad or notepad++
because both OPEN them - there is no need to open them and load them all into memory, a proper application can read them line by line.
Is SSIS the right way to deal with this?
No. SImply because the title is: Importing huge data from text file to sql using c# winforms
As Winforms can do that effectively - I am inserting around 100.000 rows into a database - in C# with quit eeasy coding (except some pages and a day to get sqlbulkcopy to work properly) and you say nothing about any transformations, SSIS just is another not needed technology AND makes things complicated (as in: more to install, or hav a packag on the server but then find a location for the file that the server can reach etc.
I am all for SSIS and if you have a larger SSIS infrastructure or do a lot of processing etc. and it makes architectural sense in a larger context - yes. But as the question stands, without additional reasons - absolutely not.
Heck, there is a good chance you can load the whole thing in one command into SQL server as SQL Server has some CSV processing capabilities:
http://blog.sqlauthority.com/2008/02/06/sql-server-import-csv-file-into-sql-server-using-bulk-insert-load-comma-delimited-file-into-sql-server/