that's just sad...
If I understand correctly, any feature ASUS takes from you and puts it in their code, in theory should simplify your work and allow you to work on other features -am I correct?
It depends. Asus and I have quite different priorities. They must release a product for a large variety of customers, to sell to as many different type of users as they can, and be prepared to provide tech support for it. Having a level 1 tech support trying to answer questions on how to properly configure tls-auth through HMAC is simply unrealist. Because of this, they must provide a web interface that is as simple as possible.
In my case, I target average to advanced home users, and don't need to satisfy the largest amount of users possible since my goal isn't to sell a product to as many users as possible. That means while I keep the simplicity of their webui (unlike DD-WRT's sea of options), I can add a little extra in terms of configurability. It makes it harder to provide support afterwards, which is why I increasingly rely on the community to support itself.
In some cases, Asus merging it in the base code makes my life easier. For example, their addition of the WOL page allowed me to drop my whole WOL code (cause theirs was far better implemented - mine was the very first feature I had implemented, so it wasn't as well integrated). Their Connections page almost completely replaced mine, with a minor difference between both.
In OpenVPN's case however, we both had to make decisions about design according to our respective goals. My original webui would be next to impossible to support by their tech support department, and their webui wasn't suitable my personal design goals.
To my knowledge, PIA does not really require anything very unusual - for one, it worked fine with much older Merlin's firmwares - and very reliably!
if ASUS wants to offer a oversimplified interface for novice users - fine, it is a good idea as most people are clueless about these things anyway; however they should offer full blown "advanced menu" for cases like this one - do I make sense?
They did it for the server side, so maybe the client side implementation is still a work-in-progress. Give them time, OpenVPN was a fairly major feature to add to their firmware.
Personally, I'm already both surprised and impressed that they decided to add OpenVPN at all. When asked by users which features I thought likely to see appearing in Asuswrt, I used to say that OpenVPN was highly unlikely to ever happen. Looks like I was wrong.