Season 2 used Zyu 2 footage. Power Rangers Season 1 did so well that Fox commissoned more episodes then they originally ordered. So Toei shot extra action footage with the Zuyo costumes/zords. These we're used at the end of of Season 1 and in Season 2. They did do US only scenes. Especially in season 2 and 3. So thats why Tommy could still have his powers in "Green No More" and Kim having a Shark Cycle. The Shark Cycles we're actually all US footage.
As for comparing Sentai to PR. Some seasons try to adapt Sentai closely. To where they actually shoot US scenes to match the sentai. Like a lot of Time Force, Wild Force, and Mystic Force. But other seasons try to use the Sentai footage to tell there own story. With original US footage. MMPR Seasons 2 and 3 we're very much like this. They did a ton more american footage during that point. Space and Galaxy are examples of Ranger seasons that totally did there own thing ( Since MEgaranger and Gingamen we're not about Space Rangers).
Super Sentai can get away with more then PR. Since children's standards and practices don't censor as much out there. Sentai can be more violent and have darker storylines. But there is still plenty of comedy and camp. The target audience actually is for younger children then PR is. Sentai tends to not really have a tight continuity ( outsite of team ups). Unlike early PR had ( obviously now they are similar to Sentai, with little inter-season continuity besides team ups).
A friend of mine is doing a site to compare Sentai to PR. Its just starting though and not complete. But you can check it out. He has MMPR- Zeo/ Zyuranger-Ohranger so far.
http://www.rangerarchive.com