So, the first mistake you made was to NOT make a full backup. That is the biggest mistake you could make and negates everything else in terms of blaming someone else for your problem.
True.
I do not blame anybody but myself. I assumed that a SEED backup was enough.
It is, but not for blackbytes.
I have a lot of different cryptos, but most of them are stored on my ledger nano hardware wallets and the seed is protected with multiple cryptosteels.
All other are backed up with encrypted wallets on multiple devices and locations.
Byteball was the "only" special one -> SEED, but not enough to recover all assets.
Since you had your seed, you knew up front that a backup of a seed only would only restore bytes (not blackbytes), as it tells you exactly that during the seed backup (and recovery).
I store all my SEEDs within Keepass. And the byteball seed was created a long time ago -> e.g. I just forgot the disclaimer about blackbytes.
Why would you delete your appdata (wallet folder) just because of a one time error? That's another mistake (second) in that even if the wallet has a problem, it can be fixed. So, a backup (simply moving the folder) is preferred to deleting and then hoping to magically get the funds to reappear.
Why? Delete the appdata folder was to ensure that I can install the new version without old artifacts that could cause trouble and backup with the SEED.