It's a bit worse than this if you are on EHU or Solar to try and keep up the Leisure Battery you will lose all that charge as soon as you drive the van
See my post here:
Hi, One question. Actually I have the default battery coming with the van: AGM battery of 100ah (the battery is only 1 year old). I have been looking for information, but it is not very clear: some places says if you want an extra battery, you need to discard your current battery. That you...
www.t6forum.com
As you say basic split charge approaches sort of work if your use of the van is such that you don't really use the leisure battery much when touring and are on EHU a lot when camping as that works with the restricted charge to 80%. And if you are only on EHU infrequently then the very basic charger isn't going to get much chance to be unkind to the battery, though to be fair the external CB516 looks better than most, mostly it will be charged by the van which does understand AGM charging (even if it doesn't charge to full to do the regenerative braking) Mostly I think folks notice the compromises when they use the van mostly as a camper and then decide to branch out and do more off grid.
Start Stop systems in campers are not really new anymore, it's a bit disappointing that the all in one type systems still view DC-DC as not necessary at worst or an optional extra at best. It's a price sensitive market though and you don't notice the compromises until quite a while after purchase so I can see why lots of folks end up with them.