Read those articles and the biggest thing they were trying to say is if you wean early, you can feed a lesser quality feed to the cow since she will have a lower nutrient requirement if she is not lactating.. and stressed .... that it was for mostly drought stressed situations...
BUT.... the did not talk about the ACTUAL COST that it will take to get the calf up and going... and let me tell you something after having a friend that is involved in one of the land grant colleges that do all these "experiments" ..... they do not worry about the cost to the calf in the long run.... these are just that... experimental studies to prove that it "can be done"... not that it is a practical reality for 99% of the farmers.
That is a bunch of hog wash for nearly all situations.... sure, anyone can do it... he// you are doing it... with yours... and actually they are doing good considering....
And by the way, after looking at the first videos of the calves when you got them... I can honestly say you did one bang up job getting them to look as decent as they do... they were not weaned calves, they were pulled off their mommas, for whatever reasons, as babies... I would say they were not 8 weeks old or so... NO WHERE NEAR ready to be weaned... maybe they were just culling cows due to lack of feed or whatever... but those calves should have been on a high protein mostly grain diet right off the bat... with limited hay of the best quality grass hay you could find..... I will bet they did not weigh in the 200-250 lb range.....
Sorry, this got my dander up a bit. Would you feed your kid just "dry food" at the equivalent of 6 months or a year old???? No bottle of milk after 6 months old or something??? that is what pulling a calf off a cow at that size is like.
Understand that sometimes calves will not take a bottle after being on a cow for 6-8 weeks... and I get that it might be very hard to get them to suck... that is where the straddling, and backing them in a corner and forcing the situation for many feeding sometimes will eventually get the light bulb to come on... OH, THIS TASTES GOOD..... because a bottle is nothing like a real teat.... But the alternative is good calf ration grain... good protein, and some very "soft " bladey kind of grass hay....
We wean in the 7-9 month old calf age range, and most cows will be bred and ready to calve right back at the 365 day range... and the cow did all the work to get that calf to weaning size and after a few days of being mad that they don't have momma, will go to eating and never miss a lick.
Bulls go in with the cows at approx 60 days after they have calved... and for the most part they are cycling then. Always some exceptions... but I would rather feed the cow even in drought conditions to get the calf up to 4-5 months before considering weaning off the calf... and they would have to be going into a creep feeder so they know what feed is and can transition easier...
In your case of bought calves, they should have been put immediately on some good 16-18% calf feed, molasses added for some sweetness and fast digestible energy.... to get them to transition to feed... and I would have been doing my dam#@dest to get them to take a bottle and feeding them at least once a day on milk for another couple of weeks as they got used to "real feed".