Is it in the best interest of supervisors that his/her students publish their research results in top journals?
First of all, journal quality is not an objective thing (measures like acceptance rate and impact factor and so on really do not mean that much, and can be gamed).  There isn't necessarily universal agreement about which journals are "top-tier".  So consider the possibility that your supervisor simply has a different opinion about the reputation of these journals than you do.

The advisor does have a responsibility to give advice that they believe will be beneficial to students, including advice about where to publish.  (Of course, the student also has a responsibility to educate themselves about publication options as best they can, ask questions to try to understand the advisor's suggestions, and speak up if they disagree.)  I'm not sure what you mean about whether it is in the advisor's "best interest".  It is not like they will get paid more if you publish in Acta, but it does generally reflect well on an advisor if their students are successful.

But there is a serious trade-off of submitting to top journals: time to acceptance.  The peer review process in math is much slower than in many other fields, and top journals are very selective.  Even if your paper is "good enough" for a top journal, that doesn't mean that it will be accepted by the first one you submit to, and it may be under review for several months before being rejected.  Then you have to start over.  As a PhD student, you really want to have papers accepted before you begin to apply for postdocs or other jobs.  A paper that hasn't been accepted anywhere, even if it's an awesome paper, doesn't help your job prospects much, because there's no independent confirmation that it's awesome.

So at this particular stage of your career, it could be very sensible to submit your work to a less-than-top journal, even if you think it has a chance to be accepted somewhere better, because it's more important to get it accepted fast, without having to go through several submit/review/reject cycles with different journals.  This is something your advisor ought to take into account when suggesting journals.  But it's a balancing act between the considerations of "publish in the best possible place" and "get accepted on the first try", and you should of course speak up if you have a different opinion about how to balance those.

(If your advisor is a co-author, this same balancing act could apply to them as well.  For instance, they might have a promotion decision coming up, and they want to have the paper accepted somewhere before that happens.  Sometimes different authors may have conflicting needs in this regard, and they have to reach agreement somehow.  Personally I think that the needs of more junior authors, such as PhD students, ought to be weighted more heavily, but that is just me.)

I also want to comment on the "corresponding author" question.  People around the world seem to have different opinions about what it means to be corresponding author.  In my part of the world (US), it's my impression that being corresponding author only means what it says: this is the author who corresponded with the journal (sent in the submission, filled out the forms, etc), and who is the best person for a reader to reach if they have questions about the paper.  Around here, it doesn't carry any particular prestige, and it isn't meant to imply that "this person did most of the work".  So on that basis, I wouldn't say that there was anything wrong with your advisor being corresponding author.  (For one thing, your advisor probably has a more stable email address, since you are going to graduate before too long.)  There may be some benefit to being corresponding author as a student, just to get practice with the journal submission process, but it's not really a reputation benefit.

(If "corresponding author" has a different connotation among people in your part of the world, or more importantly, the part of the world where you intend to apply for postdocs, then the previous paragraph may not apply to you.)