That's often the usual situation for
Dutch people. I wouldn't start calling
Thomas "
Tom", unless of course he'd ask me or if he'd have introduced himself as
Tom, and I would have only later found out that it's a nickname for
Thomas.
Also, using 3 syllable names without a nickname is common enough for people not to start bullshitting about a name being too long, bc they can't be bothered to take the extra effort of saying an 'extra' syllable.
A 4 syllable name might get shortened if there's a very obvious alternative (ie.
Alexander "
Alex"), but I wouldn't start calling a guy
Alex unless I know it's okay. I feel surprisingly normal actually about using the full form of a name.