because its now only the "half" of the whole techs researchable
Sorry but that is nonsense, there aren't that many Specializations, half of the tech tree is a gross exageration.
The Idea is good that you have to specialize you and can't resaurch all the techs in one game but now you are finished with all the techs after
a "couple" of turns. That reduce the fun extrem I feel so...
Another silly exageration, you should avoid these as it prevents people taking your point seriously.
If you can research all specializations they literally become pointless, seriously just dump them and add the current ones as normal techs on the tech tree. That is in essence what you are asking for when you say you want to be able to research them all.
Making people choose in this way gives you an extra strategic choice to make, and in a stratergy game extra strategic choices are good.
As for the length of the tech tree, so mod it and add more techs yourself, or mod it and get rid of the specializations and add them back in as normal techs.
The way they have made specilizations work now is also great for modders in general as it allows them an extra choice in structuring custom tech trees.
I know not everyone supports this and there is no design decision you can make that some people won't object to but it actually makes the game richer, not poorer in possibility IMO so I support them in this.