No companies compete solely with endorsements. That's not the metric. The point is endorsements
do drive sales.
In the 80s there was a sea change in hard rock drumming to Tama, led by the public use of their kits by Lars Ulrich, Neil Peart, Dave Lombardo and Steve Riley. It had a huge impact on sales at the time.
Lots of small companies today partner with musicians that mutually benefit both sides. It might be with smaller or up-and-coming artists with niche fandom, to compete more affordably with Fender's bigger roster of popular endorsers. JHS made
a distortion/overdrive pedal by partnering with Brazilian guitarist Lari Basilio. Reverend partnered with 90s-era musicians like Mike Watt and Meshell Ndegeocello for signature models. Schecter recently made a deal with Charles Berthoud.
But you don't need to go as far as making a signature instrument just to make a simple endorsement deal.