Firestar was also sad about Tigerstar's death in
The Darkest Hour and asked for his strength before the battle against BloodClan while Longtail had this to say about his former friend:
"Tigerstar was a great warrior. He was the strongest cat in the forest and the best fighter. When I was a young cat, I thought he would be the next leader of ThunderClan. I wanted to be just like him."
―Longtail to Foxkit and Icekit Outcast, page 28
Then there is this in his Trivia section on the Warriors Wiki:
In Secrets of the Clans, a 2007 field guide, Tigerstar is listed as one of ShadowClan's significant leaders and is described as ambitious, crafty, charismatic, and a brilliant fighter.
Tigerstar is also seen by the overall narrative as someone who wasted his own potential by using it in the wrong way which is included in this essay by the former editor/author Vicky Holmes:
warriors.fandom.com/wiki/Tigerstar:_Heart_of_Evil%3F"If you look past his murderous plots to overthrow Bluestar and destroy Firestar's credibility, you'll find a brave, skilled warrior, utterly committed to protecting his Clan, proud of his kits, respectful of his ancestors, and loyal to the things that are most important to him."
— Victoria Holmes, in Tigerstar: Heart of Evil?
The point of Brambleclaw saying this about his father is not to convince anyone of Tigerstar's nonexistent innocence in contributing to his own downfall but rather to emphasize on how things could've been different for him if he had just been patient and used his strength for the good of his Clan instead of only to aid himself.
I'm a fan of Tigerstar as a villain because there is such a thing called "love to hate someone" and he is definitely a character who this applies to almost perfectly.