Food is of the least concern when you’re f2p. Unless you haven’t been upgrading your food storages but that is easy and quick to solve anyways.
Everyone has access to grind map levels, food is constantly pouring in from completing them, the wanted chests give you food, your watchtower gives you food… man I remember having an issue of not being able to collect anything from my farms. Seriously, food is whatever for f2p, it only really becomes an issue when you’re ascending 5 stars too early.
I’m now running TC 12 & 13, an cause of 1700 sturdy clothes, TC 19.
Had good results from TC 12, one three star per day, an 2 epics from TC 13 so far,
TC 11 is grt for fast levels as long as bkpks hold out, an TC 14-18 give me nice rares so you can fill in missed colors 
So I just got my TC20 up and running last month. I have 2 now and am working on a third.
In total I did 77 pulls on TC13. Got ten 4*. Strangely enough 2 of each color:
Wu Kong, Li Xiu, Boril, Kiril, Cyprian, Kelile, Gormek, Skittleskull, Tiburtus, Caedmon
A nice mix. I would strongly encourage any player, but particularly a F2P not to skip TC13. Without these 4*s I would not have been able to make it through the final level of the class quests or the epic level of challenge events. Probably wouldn’t have been able to finish all of the memento quests either.
Most importantly by the time my TC20 was up and running I already had a 4* rainbow defense team with emblems which lets me hang out in platinum and occasionally open in diamond.
Nobody should be skipping TC13, it takes a while to get up to speed from 13 → 20. F2P particularly should not skip it.
On the main topic’s point though, I do agree on the value of TC12 for F2P. If you paid and did summons, then you already have enough 3*s and TC12 can be skipped. But if you didn’t, then you likely have only 1 of each color if you’re lucky.
Factor in the time spent to upgrade your storages, production sources just to get to level 13… and then there’s upgrading one of your training camps, and researching level 13, and getting the food back up again to be able to train with the number of recruits storage needed.
It’s easy to forget the struggle. But it exists. I think TC12 serves its purpose, however short it is relative to the amount of time playing, for F2P.
I like the Tc13 in fact. Actually i am finishing to pass ib level 17. I use a lot tc13 for 4 stars heroes. I already have 3 and good one: Gormek Caedmon and Rigard. Yeah i had a lot of 3 stars heroes but this is still very nice to have 4 stars without to be in tc20.
You got extremely lucky. In that time, I pulled 2 4* heroes (sabina and Li). While tc13 is better than nothing, tc20 is something that needs to be done ASAP.