Allowing for more varied MP costs takes no more than switching DA from "next spender free" to "next X-gauge's-worth of spending free". We've already seen changes similar to that in other jobs once a reason for that small extra layer of precision was added. That DA currently only affected Edge/Flood does not mean it must only ever affect Edge/Flood. It just means that there is at present nothing else for it to affect.
Under the current system, we're locked into only having Edge/Flood on MP.
No. No, we are not. There is
currently NOTHING ELSE on MP. Given there is
currently NOTHING ELSE to spend MP, DA only affects what's on MP (Edge/Flood). That does not mean it can
only ever affect what is
currently on MP.
Unless you're insisting that TBN was designed from the start to purposely (dis)favor certain currently inexistant spenders over (or, in favor of) others, there is no reason to think they'd use new ability additions to add complexity (works on this but not that) to TBN. Far more likely, we'd simply have its gameplay affects translated over by simply, in essence, modernizing its language and no longer shortcutting its procedure to take advantage of very limited surroundings.
We can't discuss situational alternatives to TBN (like old RI vs NF, or Cover vs Intervention) without discussing how to implement a DA-like aspect or make up for not having one.
Yes, that's how alternatives work. They take into account the full power of whatever they're competing against. What is shocking about this? You already have to do this for every other alternative. Why would it suddenly be so bad that you have to do this for TBN, just as you would for anything else?