I think I understand what We Three means (please do correct me if I've misunderstood though!) - looking at your post I feel there is probably quite a bit more going on that a simple dummy dependence leading to your night wakings and I'm not sure that taking the dummy away is necessarily going to solve things for you entirely.
Firstly, from a BW point of view I would say the routine needs some adjusting. For a 6 month old we would expect LOs to be somewhere around 2h45-3h or so A time and probably somewhere in the midst of transitioning from 3-2 naps. Your LO on the routine you posted is having some very short A times - less than 2 hours at times and max of about 2h30. A 'typical' BW routine on 2 naps at this age would be something like WU 7, Naps 10-11.30 and 2.30-4, with BT at 7pm. A 3 nap routine with slightly shorter A times would be more like WU 7, Nap 9.30-11, nap 1.30-3, short CN around 5.30 with BT at 7.30/8 (longer than a 12h day common in the run up to nap transitions). Sometimes keeping LO on too young of a routine can contribute to night wakings as their A times are short and they don't get properly tired enough to sleep soundly at night.
I would probably suggest to work on gently pushing his A times, starting with the first one of the day, and working towards 2 naps over the next month or so. From where you are now perhaps start at the 2h mark for first A time, increasing by 10-15 mins every 3-4 days until you get up to closer to 3h. You can work on all A times at once if you wish, but you'll have to play things a little by ear until he gets used to being awake for longer.
In terms of how you are settling him I think perhaps you might have a combined breast/dummy dependence (prop) for sleeping. You've made what sounds like great progress in the last few days (well done!
) if he is now able to settle in his cot with some gentle reassurance, but the goal ideally is to have him fully awake going down and settling himself from there - i.e. from 'eyes open and ready to party' rather than 'eyes open but could drift off any second'. It sounds like perhaps he is using you/feed/dummy to wind down and get himself in the sleepy zone, so although he's technically doing the last bit of sleep on his own, he's getting 90% of the way there with help. He's also feeding quite a bit at night for a 6 month old - now I say that with caution as every baby/Mum breastfeeding relationship is different and demand feeding is encouraged, but 4 feeds overnight at roughly 2-2.5h intervals sounds more like he is asking for the breast to help him resettle each time he comes into a light sleep cycle than really being genuinely hungry every time.
Weaning night feeds can be a little tricky to advise on with a 6 month old who is not yet established fully on solids, but as a base I wouldn't expect him to need feeds more frequently at night than during the day. So say every 4h or so? Which would mean 2 feeds at night was pretty reasonable for him for now. If he wakes and it's been significantly less than 4h I would settle using the shh pat/PUPD you've been using until he goes back to sleep. It may be easier for your DH to do this. If it's been a good 4h or so since a feed then you could feed him immediately and put him back down - if he feeds to sleep during a proper night feed (as opposed to a comfort suck) that's less of an issue if he can settle himself at other times.
Is that at all helpful?