As your question implies, this matter is an issue of opinion, and it can be argued either way, depending on your stance. I'll give you my thoughts, but keep in mind that you can choose whatever position you'd like. Just make sure that you have ways of backing up your opinion.
In my mind, Asian Americans are definitely lumped into one big group. I see this a few ways, but one of the main ways is through official and legal forms. For instance, often, official forms like censuses, school documents, etc. will ask you to check a box for your race. Typically, this will include options like White, Hispanic, African American and Asian American. This ends up forcing Asian people (which is a massive group of people hailing from a slew of different countries and cultures) into, literally, one box. The same goes for other races; if you're Jamaican, you have to be African American. This creates an effect where individual identities and cultures are erased in favor of a more simplified and generalized race indicator.
I also believe that Asian Americans are lumped together into one group in American pop culture. Often, there is very little effort put forth in media to distinguish between different Asian cultures. Even a recent movie that was lauded for being progressive, Crazy Rich Asians, demonstrates this to a certain extent. To American viewers, all Asian people are merely Asian, no further information or ethnic classification is necessary. This is also evidenced historically, where racial slurs for Japanese people have been extended to other Asian races as well.