رضا:
Merriam-Webster lists breaststroke with no hyphen. But you're correct about the syllabification. I certainly can't think of a word with more than three consonants at the beginning of a syllable or more than four at the end.

Regarding assimilation: if you're saying that Americans often pronounce d+y (e.g. in "incredulous" or "did you") as /j/, then I agree with you. But it sounds as though you're saying that Americans always pronounce d+y as /j/. As an American who pays attention to such things, I can tell you that this is simply not true. The degree of assimilation depends on many factors, including but not limited to the speaker's nationality.

Certainly there are great differences in pronunciation between the U.S. and England, but there is also considerable regional variation within each country. The next time you run into a n Englishman and a Bostonian and a Texan, have them all say, "Park the car in Harvard Yard," and let us know which two sound most alike.