I own and operate a new aircraft with no trim tabs. No arm fatigue issue because the entire horizontal stab is moved for pitch trim. You will find that many aircraft, gliders, small single engine, and large transport, do not use trim tabs. They do all have some means of trimmmg out the pitch control forces though and I don't know if/when this was introduced in WW1 aircraft.
This thread says several WW1 aircraft had pitch trim. -
https://bbs.hitechcreations.com/smf/...opic=283906.15