I completely disagree. Longevity is inspired by playing the campaign first.
You want to create your dream park? Earn the right to do that. I've played the Rollercoaster Tycoon & Zoo Tycoon games, and more often than not, I've got straight to sandbox to create a limitless park and I've quickly got bored once all is said and done. Frontier are making people play the game, rather than rushing to the end content, and I think that's the perfect way to go.
I'm the exact opposite, lol. If I have to play the campaign, then by the time that's done - I don't really want to play anymore as I've seen it all. Planet Coaster is nice in that it gives you the option to do the "campaign", do challenges (this is really fun), or just go full sandbox (which I can't stick with, as I get bored; same as you) whenever you like, so if I start tiring of challenges, do the campaign; or play around in sandbox for a bit.
I would have liked this in JW:E.
I earned the right to create my dream park by buying the game. That said, I'd play the campaign whether fully unlocked sandbox was available at the start or not.
Still, given this clear difference in preference, I think it would have behooved Frontier to cater for both; since neither party is affected by this approach.