Curved Traveller

Yes
Hydronic or spring lifting vangs and topping lifts also can restrict the mainsheet 's action on the leach tension

 

It depends entirely on what you are trying to do with your controls. A 38'er might be designed for anywhere between one and eight crew sailing it - each with sail control responsibilities. The control scheme has to match the intended number of sailors as far as control independence is concerned. My Catalina 38 was modded by a previous owner and has a strongly upcurved, laterally straight main track. It is designed for a crew of seven. The mainsheet guy and the traveler guy are at the front of the cockpit at the companionway and the winches are on the cabin roof. The primary trimming is done with the traveler and the track curvature gives you very linear feel as far as effort vs boom end movement with the sheet being left alone - and it doesn't change the twist. With the original deck-curved traveler, you wouldn't be able to use the traveler alone for trim. It would load up too fast and unload the mainsheet and change the sail's twist. You also run out of traveler sooner, since the ends of my traveler are now about 10" off the deck and closer to the boom. Plays hell with forward visibility, though. The mainsheet geometry is somewhat weird and it took me a while to appreciate that it was designed in conjunction with the track curvature specifically to keep twist constant as the traveler was worked.

 

Internal Star Class circular vang track. I have ripped this from:
Star Class https://starclass.org/
In the early 1960’s Duarte Bello, the Star boat fittings design wizard and manufacturer, came up with the idea of a circular vang track.
Boom Vang
It is hard to imagine today, but up through the mid-1950’s the major way of keeping the boom from lifting while on the run was to have the crew sit on the boom!
Star Class | History https://starclass.org/history/star-boat-design-and-development2

 

Phil,
Same with the Catalina C30 main sheet traveler upgrade. You also have to change out the bracket and the upgrade to the end boom sheeting is 5:1. The old curve/shell back one was 3:1. You had to be very strong to adjust it and with sails powered up most likely impossible.

My old Internal Star Class is a 1954 and is no thrill running rigging, just brute force.