'undoubtedly successful' is a correct and usable phrase in written English.
You can use it to emphasize the extent of success or to conclude that something has been achieved with certainty. For example: "His approach to the problem was undoubtedly successful, as he was able to solve it in record time."
Although the Million Man March was undoubtedly successful as a convening, criticism of Farrakhan was blistering.
Chimpanzees are undoubtedly successful hunters, but the "wars" seen between neighbouring bands seem to have been brought on by human encroachment on their habitat rather than original sin.
Even 'New Right' is hard to discern, once you move away from the undoubtedly successful project mounted by Arthur Seldon and pals at the Institute of Economic Affairs to change the way we think about production and markets(2).
Another recent study found there were 95,000 adult female golfers and 40,000 juniors in England, among the highest numbers in Europe – and campaigns like This Girl Golfs were undoubtedly successful.
Although it may be a well-worn frame of reference when it comes to Fanfarlo, it is hard to escape their similarity to bands such as Arcade Fire and Clap Your Hands Say Yeah, though what makes them different is the variety of musical talent on display, combined with a full-blown – and undoubtedly successful – effort to please an audience.
They were undoubtedly "successful", though.
Some of the companies were undoubtedly substantial, successful companies.
The search for water on Mars has undoubtedly been successful.
"We share his view that soccer would undoubtedly be successful in Queens".
Some small clinics and stand-alone hospitals will undoubtedly remain successful, perhaps catering to the luxury end of health care the way gourmet restaurants do for food.
There is undoubtedly a successful dialogue between architecture, materials and art and the attention to new works, to live art, to women and international artists.
