If you're looking at hard paint with jagged edges then I'd say that one of those orbital sanders you mention isn't the best choice. They are made for a smooth finish but lack the power for heavier jobs.
I've done a lot of house painting, grew up in a body shop where I learned to work with paint and all kinds of machines, but I prefer to work with wood instead of metal like my father did. One thing I did grow accustom too is the power of the random orbital sanders like the Rotex. They are more or less the standard in the car business so from ever since I was a young boy I learned to do every possible job with them.
And to be honest, it is my opinion that with the proper skill you can do about any job with them any other sander can do. With the benefit of a lot more power and faster work. Especially on hard paint that's difficult to remove. You will have a long and hard time doing the same with an orbital sander, especially those small ones.
But ....... you say you used a putty knife to no avail, have you tried an old chisel? I always use a couple of them of various sizes, and when they are sharp there's not a strip of paint that can withstand them. Much better than a putty knife because a putty knife isn't meant to be sharp. When I meet an edge like the one on that photo, I think: chisel!
After you've done the rough work with the chisel you could best use the RTS 400 to smooth it out (if you don't want to go for a Rotex
), it's much more versatile than the 130. If you want even more versatility, get the DTS instead of the RTS, the Delta shape can do what the square can do plus tight corners.
I use the Rotex 150 and an 93x93 mm delta sander of Metabo to do all my house painting work. The DTS 400 is on top of my wish list though.
