Thanks, DN 14 contains many vague and some explicit details for an actual differentiation
Here, acela Kassapa provides details, not the Buddha. Acelas are, as Bronkhorst and Balcerowicz worked out, probably Ajivikas or ‘sky-clad’ Jains. In DN 25 the same passage is spoken by the wanderer Nigrodha. In MN 12 by the Buddha about his own bodhisattva-practice. In MN 45, MN 51, MN 60 by the Buddha. In MN 94 by a bhikkhu Udena. And in AN 3.156–162 and AN 4.198 by anonymous speakers.
The speaker-situation adds some complexity to it, but let’s assume that the passage describes what the suttas consider ‘wrong self-mortification’. Let’s see what it is exactly:
They go naked, ignoring conventions
Taken literally, it means going naked would be wrong mortification.
They lick their hands
It’s not clear from the passage what it means. But we know that Digambara Jain monks didn’t use a bowl, so this might criticize the practice to receive alms-food directly into the hands.
they don’t come or wait when asked
It’s not clear from the text why that would be wrong or excessive. Maybe it was considered offensive. At least Mahavira is described to have received abuse for similar behavior.
They don’t consent to food brought to them, or food prepared on purpose for them, or an invitation for a meal.
Again, here the argument seems that it goes against social convention and politeness rather an excessive self-mortification.
They don’t receive anything from a pot or bowl; or from someone who keeps sheep, or who has a weapon or a shovel in their home; or where a couple is eating; or where there is a woman who is pregnant, breastfeeding, or who has a man in her home; or where there’s a dog waiting or flies buzzing.
Again, we can only speculate what’s the point here. There seems to be an element of ahimsa (no weapon) or some weird sense of purity, but the logic is not clear from the text itself.
They accept no fish or meat or liquor or wine, and drink no beer.
A strict vegetarianism, coupled with what is also a Buddhist rule, namely not to drugs.
They go to just one house for alms, taking just one mouthful, or two houses and two mouthfuls, up to seven houses and seven mouthfuls. They feed on one saucer a day, two saucers a day, up to seven saucers a day. They eat once a day, once every second day, up to once a week, and so on, even up to once a fortnight. They live committed to the practice of eating food at set intervals.
This seems to refer to what is seen as excessive fasting. (Btw years ago in Sri Lanka I met a Thera who was practicing very similarly, eating one day, fasting one day, then 2-2, 3-3… 14-14, then again 13-13, etc.)
Those ascetics and brahmins also consider these practices of self-mortification to be what makes someone a true ascetic or brahmin.
That’s clearly expresses an EBT-position: Asceticism and tapas are not the most essential aspects of Buddhism.
They eat herbs, millet, wild rice, poor rice, water lettuce, rice bran, scum from boiling rice, sesame flour, grass, or cow dung. They survive on forest roots and fruits, or eating fallen fruit.
Sounds like favorite items from an organic food store 
The point might be that it’s unhealthy in the long run to just eat that.
They wear robes of sunn hemp, mixed hemp, corpse-wrapping cloth, rags, lodh tree bark, antelope hide (whole or in strips), kusa grass, bark, wood-chips, human hair, horse-tail hair, or owls’ wings.
Most of these are just uncomfortable for the sake of it. Even though Mahakassapa also wore a robe made of rags.
They tear out hair and beard
Self-inflicted pain-endurance…
They constantly stand, refusing seats… They squat… They lie on a mat of thorns, making a mat of thorns their bed… They make their bed on a plank, or the bare ground. They lie only on one side. They wear dust and dirt. They stay in the open air. They sleep wherever they lay their mat. They eat unnatural things, committed to the practice of eating unnatural foods.
Again, uncomfortable for the sake of it. Possibly to overcome pain.
They don’t drink, committed to the practice of not drinking liquids.
Mahavira was supposedly not drinking for longer times. Also death by not drinking is Jain practice at the end of their path.
They’re committed to the practice of immersion in water three times a day, including the evening.
To my knowledge this is a practice of penance, to purify oneself daily. It is not clear why that is excessive, except for maybe saying that it’s superstitious and inefficient.
The biggest problem with this passage is that it’s just an enumeration of items. We don’t even know if each and every one of them is condemned, or if it’s a list of things that ‘others’ do - with the possibility that not all of them are condemned by the EBT. And if they are criticized we don’t get a rationale, except the insinnuation that it’s ‘excessive’.
