No, there is no developer ISO. Yes, you do have to manually install them. Ubuntu is made to be a distribution aimed at ease of use on the desktop meaning that the main use is word processing, etc.

To install basic development tools, run:

sudo apt install build-essential

Any other tools can be installed with:

sudo apt install tool-name

DKMS installs gcc and make automatically

DKMS (Dynamic Kernel Module Support) automatically installs gcc and make in order to compile kernel modules from manufacturer's source code. It's often necessary to compile source for some WiFi Drivers, Graphics cards, etc.

$ gcc --version
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ g++ --version
g++ (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ make --version
GNU Make 4.1
Built for x86_64-pc-linux-gnu
Copyright (C) 1988-2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

You are definitely correct that git is not installed by default however I don't consider it a programming language, more of a library system.