I agree that Barty's results against Top 100 players aren't good, but the rankings don't lie
Barty's winning streak in ITFs is too much to ignore for a 16 year old. She's improved a lot over the course of the year. The only Top 100 players Barty has played since the beginning of the year (when she was just 15 years old!) are Kvitova and Vinci, and you're delusional if you think Robson would've taken sets off them.
I'm not saying that Barty would necessarily be better than Robson, but it's not out of the question.
It's just really not right to compare a girl born in January 1994 to girls born in April/June 1996, because she won a few sets over some decent players, yet ultimately didn't win the match anyway. That's like comparing these girls to the likes of Azarenka, Radwanska and Wozniacki, going through the statistics and what they achieved at the same age. It's really barely relevant when the age gap is that wide.
Vekic's results since Tashkent have been fine?
She reached the SF of $100K Suzhou where she lost to Hsieh, and QF of $125K Pune (where she was injured and lost to Tanasugarn). She had a bad loss in the QF of $25K Seoul but Yuxuan Zhang is another good player who nobody's talked about yet in this thread. Donna easily reached the final qualifying round of the US Open (dropping just five games) so the signs were there that she was ready for a big break through. I didn't expect it so soon, but it was always going to happen.
Larcher de Brito is a player who as a 15/16 year old had several Top 100 wins (including Aga Radwanska), took sets off the likes of Serena and Kuznetsova. On the other her results on ITF level were pretty awful in comparison, she never won her first ITF until she was 18, and it was just a $25K. So I'm guessing you thought Larcher de Brito was going to be a really great player and are shocked at how bad she's doing now?
Nope. I actually didn't see MLDB being that successful but I kept an open mind because the results were good. When your head is telling you one thing and the results are saying something else an open mind is always the best policy.
Additionally, what I have been saying is that top 100 wins are a better indication that a player is heading for the top 100 than success at 25k level. In the case of MLDB, that proved true as she reached the top 100 at a very young age. But the other thing I have said is that it doesn't matter when you get to the top 100, it is certainly not a race, what matters is what you do once you are there. And MLDB rather supported that view too.
One thing that actually always left me doubtful about MLDB was her emotional state. When you see players having tantrums it usually doesn't bode well for the future. There are exceptions but a lack of emotional maturity can often be a hindrance. It certainly has been for her. That, and her size always meant that she was going to have to work that much harder than the players around her, a problem that Putintseva and to a lesser exent Barty also face. I don't say short players can't succeed in tennis, but the odds aren't stacked in their favour and they have to work twice as hard. What Errani has done this year, doesn't come easily.
I have to say, your Robson/Barty comparisons are silly too. Robson had 9 top 50 victories last year, one of them was against Roberta Vinci as a matter of fact. Suggesting Barty who is playing a diet of some of the easiest 25ks on the planet in Australia is at this level is risible. Let me be clear. Ashleigh is 16, she is doing very well for someone who is sixteen winning loads of Aussie 25ks. But there is a vast difference between between beating the Tammi Patterson's and Sally Peers's of this world and beating top 100, let alone top 50 players. And Barty has shown no sign of being close to beating established WTA tour pros. That's not a big problem right now. She is 16. She has time. Another year on the tour and I expect she will be that much stronger.
I must add though, I don't believe Barty is even at the level of play Robson was on at that age but if you have read everything I've written I don't think that matters much anyway. Barty will in all likelihood establish herself on the main tour. I don't believe it will be next year though. She has a lot of improving to do. Once there we will see how she performs. Given her physical size, I would say the odds of her being more successful than Robson are small, not miniscule small but in the 10-20% range.
Donna Vekic? She is another matter, and it is true I might be being too cautious on her. She has a much better shot at breaking through next year than does Barty. Her results in Tashkent were amazing. But I want to see her get a few more decent wins before I'm really sold that she is going to be comfortable playing next year on the main tour which given her current ranking is what we can expect to attempt. I suspect she needs a little more time to come good and she might fight it pretty tough on the main tour to begin with. We will see. That said, she obviously has as good potential as any player in the game right now and in the long run I expect her to do just fine.