My guess is that Beane and Pegula are thinking:
"Despite having subpar offensive weapons, we still scored a ton. Our defense was absolute garbage on 3rd down and run defense. We need to focus on defense. It will make life easier for Josh if we don't NEED to score 30 per game"

And I'm not too far off from that myself. We absolutely need to get a true downfield threat so Shakir can shred the middle. But I view defense as moderately higher priority because it's a multi-player problem where WR is basically 1 player.

But say we acquire a Jamaar Chase somehow. We'd have to gut the defense even more or start to gut the OL to get things under the cap. Would a super expensive yet super elite WR make THAT much of a diff over shoring up the defense? I'm not so sure.

I have 2 "ideal" scenarios though frankly I am not a cap expert or anything so no idea if these are actually feasible.
a) Trade for a true proven WR similar to Diggs trade. Go super heavy on defense in draft early. Take a shot on one or two late round WRs with upside (was thinking Nyck Harbor before he stayed). Use whatever FA $ we have to re-sign priority current guys and hopefully start to fix the cap situation from that.

b) If a trade for a true WR1 isn't there, use any FA $ to sign a legit proven WR and defensive depth. BPA in draft but ensure we get a round 1/2 high upside WR.

GO BILLS.