As far as I'm aware most of the meddling came down to three players in Brands time here Iwobi, James, and El Ghazi (which was after Brands).
Brands made plenty of his own mistakes which Thelwell has now inherited.
Brands just added to the problems we had under Walsh. Instead of buying overpriced British players and sticking them on big contracts he did it with foreign lads. He added Mina, Gomes, Delph, Allan, Doucoure, and G'Bamin who are all likely to leave for free after their overpriced contracts expire.
Brands has since said in interviews it became difficult for him to implement a wage structure as Moshiri was offering large contracts out to players while he was negotiating with others. Agents talk and then the players would all ask for more money. However, worth remembering this is Brands also protecting his own reputation.
In terms of the signings you've listed:
Allan - Carlo's pick
Mina, Gomes - not sure anyone would argue with those signings at the time. Contracts probs similar to what they had at Barca. My criticism here would be that the club shouldn't have been swayed by fan opinion and not brought in Gomes on a perm.
Gbamin - highly rated player from Germany, absolutely nobody could have predicted the injuries which has basically killed of him career at this level.
Delph - brought in to support the transition in midfielder following Gueye departure. Had only missed 8 games the previous season through injury. Turned into a disaster (although played a pivotal roll the turn of form that kept us up last year.
Doucoure - hot and cold. Wouldn't say he has been a poor signing though?
I think what we all forget as fans is there are so many variables when signing players that its a very difficult role at any club. You could buy a player that is literally perfect on paper who bombs in the league, then flourishes elsewhere. Or like Gbamin, gets crocked for two years. The blame ultimately goes to the door of the DOF but not sure there is much he can do?
My biggest criticism of Brands is that he didn't look to take more control when Carlo left and instead was happy to stay that summer. He should have walked out then rather then halfway through the season.