So you have no actual argument outside of NUH UH. Glad we cleared that up.
There's plenty of cutscene evidence of mages (specifically Khadgar) using arcane magic to block specific attacks. Time magic has previous been a self-healing mechanic for mages (altered time in WoTLK). All it needs is magically enhanced robes to increase defense (probably via a passive trait) and you have a basic tanking toolkit.