I dont believe a brelvi sect exists, because before Ahmed Raza Khan Hanafi Qadri was born people issued fatwas against wahabism and deobandism in British India, he only continued their path of opposing the 2 new reformists movements of Ahle Hadith and Deobandis and defended the old traditional Islam, however he did give strict fatwas against the corrupt sufi group practises, but the Islam which was here for 1000 years, the ottoman Islam etc was the correct one and he defended it.
His opponents had no leg to stand on so they used the media power to declare the old Islam as brelvi Islam, even though we have a rich Islamic history and some great mujaddid ulema such
en.wikipedia.org
He was the first traditional sunni ulema who issued fatwa against the new reformists movement. Ahmad raza khan wasn't even born then.
en.wikipedia.org
And your 100% correct. What matters is do your duty as a Muslim, be a good person and spread peace. End of story. The sufi saints were very peaceful people so if their followers are beating people up then that means they're jahil who only follow in name but not practises. Unfortunately people find anything to fight over, be it religion, gang wars, tribal wars, drugs and these people are doing the same.
Regarding getting offended, the fact is some people on purpose like to attack the blessed Islamic personalities, this is so they can get a reaction and then do propaganda. I have people in families who say Quran and Sunnah 24 7 but then make snide comments calling grandparents as mushriks. Its very offensive if you do indeed love them. I just stay away from them rather than fight.
The same way how people in the west attack Holy Prophet peace be upon him personality, they do it on purpose to get a reaction.
These people attacking someone for not accepting the karamats are idiots, they need to be punished, unless he was asking for trouble, I don't really know what happened, normally I seen so many people coming to Sunni/brelvi mosques and challenging the molvis and calling people of shirk but no one used violence.
We had suicide bombing taking place in Data darbar but no sunni/brelvi used violence or took revenge.