I just realized, I do things you mentioned a lot, but never found it tedious, to be honest. May be I am just used to mobiles.
Reading the full fat version on mobile is tolerable, it's the writing, namely trimming to quote, that's agonising. You have to wait for the wee markers to show up holding your finger down, make sure you don't lose them or misplace them and more often than not they jump and you've deleted far too much. These days I try to wait until I'm near something with a mouse.
I don't know how or whether an app could address that. Dunno about iOS but there are a lot of things about Android that are still unwieldy enough to make my ovaries ache.
It's not really as much as a problem with needing an APP, it's just the mobile version (or any smaller version for that matter) hasn't been touched, so it just takes the regular site and shrinks it down.
Go on another popular web site, eg cointelegraph for an example. The entire UI is changed and it's formatted in a way that is comfortable. Bitcointalk isn't designed in this way.
A mobile app would be good though. The main issues are with the quote buttons being so hard to use, the overall UI and look of the site on mobile (zooming in and scrolling left and right to see posts is really annoying, personally). An app would be very hard to build to be honest though.