OP, it looks like you're actually struggling at least in part because of your Coli dragons!
I could only find two level 25 dragons; both were statted in ways that are sub-optimal. While the Coliseum can be obscure at times, following an
optimized build, preferably with three dragons, will speed you up considerably.
When you're talking about the Coli and grinding, most people are going to use Glass Cannons as a reference. They do not have the points you've put into AGI, VIT, DEF, etc, but they hit hard and fast and that speeds battles up considerably, especially once you've got three.
You are definitely correct that the Coli isn't optimized for a party of two sub-optimally statted dragons— and my apologies if I simply missed the third! I looked through a few times but have been known to miss things. And, who knows, maybe having an optimally statted party won't make your experience any better— but honestly if someone is having that little fun in the Coli, I'd rather there be more avenues for them to spend time and get stuff on the site (i.e. Adventure Mode, which we will eventually get).
There are plenty of people who don't touch Coli and still manage to have an enjoyable experience on site. Coli stuff tends to be massively cheap after a while— because there are so many people spending so much time there that even most of the rare items become commonplace, and the ultra-rare items are going to be hard for anyone to find for a reason. Pretty Pink Mums for the Blossom gene retain value even now because Gathering is limited; every trade/Baldwin item, as well as genes, from the Coli absolutely tanks after a while, which makes it pretty accessible to non-Coli players!
If you really do want to Coli, I definitely recommend optimizing your builds. It doesn't seem like it would do a lot, but even a little bit of time save is a lot. Ideally you should be able to one-shot enemies in Training Fields and Woodland Path with Scratch— Woodland Path gives you a fast, easy place to get food and loot. Past that, you should be able to one-shot Eliminate with the middle venues. While it looks like you only have one Eliminate, that still speeds up your battles a lot. And finally, you should be able to Scratch-eliminate everything else.
The exception, obviously, being if you have your Eliminate dragon statted as a 2-fodder trainer— which they are not, currently. In that instance, battles will be a bit slower, but training your other dragon(s) as farmers will still make a difference with speed— just not as much.
It's also worth saying that FR already drastically upped the drop rates from what they were originally, when even food was rare! You should be getting an item of food from almost every enemy defeated these days, with trinkets being mildly rarer but not by much; if you're not getting those, that's a bug, not a feature, and might be worth going on Bug Reports if you've been seeing the same pattern consistently for years. Going fast, with optimized dragons, should make grinding for food very easy. Rare loot is, of course, much rarer, but that's by design and not something that needs to be fixed. I find that even if I only have time for a few battles per day I'm getting something for my troubles, and it doesn't take very long at all.