Tips for starting a new research direction
So the reviewers take unusually long time, don't understand parts of your work, or don't see the merit in it? As you say, it's a likely sign that the editors have a hard time finding suitable reviewers. This suggests that you should make heavier use of recommended/excluded reviewers, if the journals allow it. Pick them strategically, but also honestly, and motivate your choices. It's not necessary for all traditionalists to die if you can get more open-minded referees... On occasion, it might also be worth appealing a rejection if there are clear signs of reviewers misunderstanding the paper. Though the probability of success seems to vary a lot between fields and journals, so your mileage may vary.

It may also be the case that your papers don't have clear enough explanations of why your approach has promise or is valid. You might well explain what you're doing clearly, but fail to convince someone else that it's worth doing in the first place - especially if existing methods in the target field work fine. Typically the case for a really novel approach needs to be more convincing than that for some incremental work. Directly benchmarking it against existing methods is often useful. Try to find any patterns in reviewer responses of the "I don't see how so and so" kind and address them head on. Also try to get critical feedback from colleagues to help find any gaps in your arguments.