The crontabs currently use python3.4 to run the scripts.
However this symlinked to python3, so the two are currently equivalent.
Unless the scripts actually need version 3.4 - and no other - it does not make sense to use the specific version. Using python3 will make a Python upgrade much simpler - no need to edit all the crontabs, as they will pick up the whatever is the current version.
[If a script does specifically require Python 3.4, then it should check this and report an error.]