The ISTP's I've known are "doers" in the sense that they like to be active - Se drives them to engage the physical world. For INTP's, Ne sort of does that, but we don't necessarily have to be outside or touching things or taking things apart. We can just read something and we feel engaged. So, ISTP's seem more "active", but they are also very different than J's. The ISTP's I've known have been big procrastinators about getting things done. One friend I knew needed to fix the subfloor in the hallway of his house. One day he ripped up the carpet and threw it away. 3 weeks later, he took out 1 section of the subfloor and replaced it. A month later he took out another small section of the subfloor (same hallway) and replaced it. About 2 more weeks later, he took out the last section and replaced it. About 6 months later he replaced the carpet over the new subfloor. When an ESTJ saw all of this, he said to the ISTP, "It took you 9 months to do a job that I could have done in 4 hours. Sup with that?"
ISTP's can definitely get stuff done when they need to, but so can INTP's. But, in my experience, these 2 types are nothing like J's when it comes to "getting stuff done". J's tend to be "work first, play later". P's tend to be "play first, work later". If you have a job, you can't really do that, but that's what P's usually want or prefer.
I am very much like the ISTP's I've known - everything except the differences between Se and Ne. Se wants to "experience" the outdoors, experience "things" and "stuff" and "how to do things" and "how things work". Ne, at least for me, is more observational, more far-fetched, more dreamy, head in the clouds. Se and Ne have similar senses of humor though. They find me funny and I find them funny.