Yes, I would guess that coins sharing an algorithm with a much bigger brother (in hash rate) are particularly susceptible. Of course, the perceived security and valuation of many coins is somewhat tied together, and I can imagine many miners would avoid attacks on other (smaller brother) chains because they might end up hurting themselves as well. But it only takes one (big enough) actor to do serious damage to a smaller brother coin, possibly looking to gain financially, or maybe just to undermine its credibility/valuation. To do the latter, I would say continuously forcing many large reorgs is the way to go.