Yes it does bother me, and at the same no it does not bother me for a number of reasons. It does bother me because it means that Sakurai valued the new Mario characters over any number of other characters that he could have included/make work in the game. A ninth of the entire roster doesn't sound too bad, but when you consider there are 49 characters total it does start to sting a little more, however the only one that actually "bothers" me is Dr. Mario.
I like Dr. Mario just fine and if he was a late addition originally intended as an alt, more power to Sakurai to making him his own slot. My frustration comes from the fact that if he did he chose to put the time into a clone Mario character rather than Lucas or Wolf, who were also both semi-clones. Obviously those two require a bit more work to be implemented, and I have no idea behind the circumstances during production of the game so I can't really say much too negatively about his inclusion over them. Hell they might not even be cut for sure yet if you believe we have more characters like I do.
As for the other Mario newcomers thank god they are unique, it makes it so much easier to deal with them being on the roster. Rosalina and Luma is an interesting concept for a character and has been very well executed from what I've seen (and my personal bias towards Rosalina helps me easily support her anyway). Then Bowser Jr. in the clown car also seems to be pretty unique, and the more of it I see the more of it I will probably like and be far more accepting of. The two Mario newcomers are true newcomers and make a lot of sense when you think about it (Even though Bowser Jr. over other characters is also pretty frustrating, but again him being a unique character overrides a LOT of that frustration). The other four Mario characters absolutely should be there and with everything they've done there with Bowser for this game almost make him a newcomer is his own right. Mario has definitely gotten the love this time around, no doubt about that, and for the most part they've done it well too. I don't expect to see that many more Mario characters in future Smash games after this blow out of new content, so even if you're angry at the new Smash for Mario now, just think of it as a promise for more newcomers from other series next time! (It helps a little at least)