De La Warr is a strange venue at the best of times so I don’t read too much into crowd sizes there - always obviously full,of people travelling from Brighton, the day of the week therefore makes a massive difference p. Those who do make it, though are rewarded with an amazing venue and smaller crowds, coupled with the fact that crowds tend to be good as the extra effort required sorts the wheat from the chafe. Have seen some of my best ever gigs there (Yo LaTengo blowing the roof of the venue to about 150 people a very special memory).
Though Grizzly Bear were excellent - new stuff slotted in well, althouhnprobbaly enjoyed the songs with 2 guitarists the most.
Think Grizzly Bear will be fine - as already said they’ll be able to fill next summer with decent size festival slots and will soon therefor be perceived as big as ever.