This is true, of course. It took me forever to find an ERD tool that worked the way I wanted to, and it took a few weeks to really learn it.
ModelRight (the one I really like) is a bit pricey. For the SQL-Server only version it’s about $600. Having said that ModelRight paid for itself very quickly. I’m a lone-wolf developer/DBA and using this program gave me a force-multiplier equal to hiring two junior DBAs.
It isn’t just about drawing pretty pictures. ModelRight is a CADD tool for database design, not only does it allow you to create the diagram proper, but use that diagram to create the scripts that create the database, alter it, and maintain a detailed data dictionary during initial design. It lets you create user-defined data types (translated to native types in scripts) that automatically set constraints and defaults, set table constraints/indexes with naming conventions you can tailor, set up foreign constraints, and allow you to script it all with a single keystroke.
I operate on a severely constrained budget, but tools like this cost a pittance when compared to the salaries of two DBAs–and it’s a sunk cost, not a recurring one.
I pick my tools carefully. Between ModelRight and Redgate’s SQL Compare/SQL Data Compare it’s like having a construction crew with heavy equipment building a canal vs me on my lonesome with a teaspoon…
The fact I can reverse-engineer third-party databases is just icing on the cake. Since, you know, I needed the tool for development anyway.