A few words on this also from a developer's perspective.
I'm pretty sure that when PGM started using Delphi it was sold and seen as an upgrade to whatever language they used before ... I guess Borland C or Borland Pascal as Delphi was then produced and sold by Borland as an upgrade to a fourth-generation language.
From Embrocadero's website: "Delphi® is the world's most advanced integrated IDE for rapidly developing native high-performance multi-platform applications using powerful visual design tools and features developers love.". It claims to support all major platforms including Windows, MacOS, Linux, Android and iOS. It's a "RAD" (Rapid Applications Development" environment, with the implicit aims of getting a working product to market quicker on all of those platforms.
I've never used Delphi, so I can't make specific observations, only observations about other RAD platforms I've used.
On the platforms I've used, I've generally found that, yes, they get the product to market quicker
from a standing start, but that they seem to become more and more difficult to manage over the lifetime of the product because one is permanently trying to make changes where some, maybe many, of the consequences of those changes are tucked away inside the environment. In addition to that, the RAD maker is making "improvements" to their product which have similar consequences. It can end up being a lot more work than one expected to maintain these things.
On JUCE and many other OpenSource software, there are understandable concerns about if or how the OpenSource licencing may impact the products licencing. Companies worry that there is a risk their own copyright may be blown apart by using it. Generally that should(*) not apply to libraries et al, which are normally under the LGPL licence, but I understand the concern. People also worry about security, but most such software is well understood and you have access to the source-code, which is often not the case with commerial libraries.
(*) "Should" is a dangerous word ... it actually means approximately nothing, e.g., there
should be peace on earth; or "It should do that, but it doesn't".
Here's a big gotcha: In principle a change from Delphi to C++ is not an upgrade, it's a downgrade. That doesn't necessarily mean that the change would be bad idea, but it certainly does raise some profound questions that only PGM can really answer.
Here's an argument, though, why the "downgrade" might still be appropriate. The programming languages C was devised in the 70s and although it's had some polishing since, it's still fundamentaly the same language. C++ is a derivative of C that has further polish, but is still fundamentally C at heart. That means these languages have been very popular indeed for fifty years. The reasons for that are several, but compactness, efficiency, the ability to do most programming tasks with it/them and their universality are key, as is the huge number of people who can use them. C and C++ are a remarkably constant foundation of today's programming and are often still very much present "under the surface" of other programming systems.