I have to repost https://news.ycombinator.com/item?id=28491963 again: My main problem with delphi: it is "too proprietary". It was a very productive IDE in the 90's or early 2000's but lost their path and never recovered. Some new versions broke compatibility with previous version's components. There was the case where you paid a good amount of money on some proprietary components and they simply wouldn't work in the…
But man are you ever right about the compatibility issues! Upgrading from Delphi 5 to the (then current) Delphi 2005 was a total nightmare. Our codebase was about 600k lines, and I will never forget the trauma of trying to get it to just build in the newer version.
The comparison with .NET codebases that "just work" from version to version is night and day, and sadly it's worth putting up with a laggy beast of an IDE to have that security around your projects.