Hi SangYup,
Welcome to Bladeforums,
The three models were designed to serve the needs and desires of different customers. Each design has particular advantages to some, and as with all things, probably some down sides to some.
The Tenacious was designed:
To be sold at a price point that was accessible to most knife people.
(Spyderco knives have become expensive for many in modern times,
but "back in the day", we were always affordable. Japanese Yen and
USA mfg costs have gone up quite a bit).
We are able to do this by mfg the Tenacious in China where the Yuan /
dollar rate is favorable to lower prices.
To have the most blade length to handle ratio. This is important to some
knife people.
To have a Walker Linerlock which offers less resistance to opening.
A machined G-10 handle scales at affordable pricing.
A size that was legal and acceptable in most areas.
A fairly thick blade for hard use.
Skeletonized liners to reduce weight.
The downside includes;
Heavier.
Made in China, which to some is negative.
Blade steel with less edge retention.
The Delica4;
A 20 year evolution of the "ideal" pocket folder.
Light
Strong (nested skeletonized steel liners)
More affordable for a Seki made model (FRN scales)
VG-10 0r ZDP-189 blade steel (superior blade materials)
Mid lock-back which has a strong self close.
Bi-directional texuring which offers good grip even with gloves.
Downides;
Still more expensive than many competitive models
Some don't like FRN handles
The Native3 is part of the continued development of the Native model.
Large finger choil (for those that like finger choils).
Light.
Strong (FRN only)
Wire pocket clip
VG-10 blade steel - hollow ground
Very ergonomic countoured handle for continued useage.
Downsides;
Still more expensive than many competitive models
Tip up clip only
hope that helps.
sal