Dialect humor/character is an acquired taste. I wouldn't say Brendel is hilarious, but with a good director, his Columbia shorts could be funny.
I have 4 of his Columbias on 16mm... I haven't screened them for a few years, but my recollection is THE BLITZ KISS (1941) and HIS WEDDING SCARE (1943), both Del Lord projects, were very enjoyable. Two directed by Jules White, OLAF'S LAST LAUGH (1942) and YUMPIN' YIMINY! (1941) were simply ok. Del Lord tended to put Brendel's character in funny situations (borrowing from Lord's Sennett roots), while White's unit tried to make Brendel's character funny.
To be fair to White, I think his attempt to pair Brendel & Shemp in PICK A PECK OF PLUMBERS (1944) is much better than its reputation. The two comics may not have had great chemistry, but each turned in good performances and made for a funny short.