I love this idea as well. Nothing but love for this change. I disliked the whole not-pop up thing (see other quests option) from the start but just never complained about it.
I like it, though I also mostly use the quest widget. But the old quest bar never worked properly for me and this one does, so I may get more in the habit of using it.
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For those who still don't want the tabs, you can amending your customCSS with this .col-12 .nav-tabs .nav-item a[href^='/quests.php'] { display: none; }
You'll still have the line that normally appears just below the tab-bar, but at least you won't have the tabs themselves anymore. This shouldn't break the rest of the site, but give me a ping if it does and I'll check if I can't find anything else you can use =)
I also play on mobile and like you I do not like that long column. I discovered, quite by accident, if you scroll right down to the bottom of the page you'll see "switch to desktop". Tap on it and it takes you to the news page. Tap the back button and you will be back at the column. Tap 'refresh' and Subeta looks normal! Dashboard on the left, bookmarks on the right and your theme rather than the site's default. You'll find you'll have to do this about once a day as its not permanent.
Now if I can figure out how to get the quest's shop search to open in another tab I'll be home free.

I am aware of the Switch Layouts link, but thank you for the advice. That was very nice of you to do! :D I had only mentioned that issue in the hopes that it might be looked into/fixed for other people that do play on their phones/tablets [sub](but it looks like it's still a long list. oh no.).[/sub]
Anyway, you can also go into the options on mobile browsers and force sites to display as their normal way, instead of their compact, mobile version. I don't know which mobile browser you may use, but here's a couple for example: Chrome: it's under the hamburger button / three dots in the corner and is a check box by Desktop site. Firefox: it's under the hamburger button / three dots in the corner and is a check box by Request desktop site. ...pretty much look for the options and see if you can find a way to force it to be desktop. haha. For me, if I want the option of normal sites when I'm on my phone, it stays checked. Maybe that would help you so you don't have to reselect the Switch Layouts so often?
As for the opening pages in a new tab, if you're using desk/laptop, you can do that by holding the ctrl button when you click or using the scroll button on the mouse, but I don't know offhand how to easily get mobile to do the same.