I've got tons of Buckeroo breeding here but haven't found the crestiness to be due to the line at all.
Of my cresty horses, one was DunIT who has Buckeroo lines but he was just too fat all over including crest from the feed program I had had him on. The mare that had the issue has no Buckeroo. None of my other (many) Buckeroo horses had the crest. They all lost weight (as most were just too fat on the senior feed, and two were cresty). DunIT and Lou lost their crest, simply by taking them off the senior pellet they'd been on and putting them instead on a low carb feed.
Additionally, mature stallions to have a bit of a thicker neck (than mares or geldings) when not sweated because that's how adult boys are... still, my Buckeroo stallions are not at all thick like you might find in a coarsely made or stocky type horse. Buckeroo is not prepotent for thick necks.
Some horses are absolutely just built thicker but the Buckeroo line is not really known for thickness, in body or in necks -- though of course you can find examples that are not what we strive for that have some Buckeroo breeding. Buckeroo is actually known for a modern look and attitude, and to be so prepotent for that modern "styling" on down through the line. The Buckeroo look can be unmistakable in nice examples even a couple-few generations removed.
(Sorry, but I have got to speak up when it comes to this particular line -- so much of my breeding goals revolve around what I see in my individual Buckeroo bred horses.)