I wouldn’t be surprised if a lot of people do wait for Smiler to open, but I don’t think that’s the sole cause of Smiler’s long queue by any means.
If that were the case; why doesn’t Wicker Man have a huge queue as well? I’d argue that ride is equally popular first thing as Smiler.
I think another factor to consider is throughput. Throughput-wise, I’d peg Smiler as one of the lowest among the big 7. If it’s on 4 trains, it gets slightly more than Rita (about 750-800pph last time I timed, and that could well have increased with the baggage hold returning), but if it’s on 3, then it’s comfortably the lowest (I have it at around 600-700pph on 3, even with the baggage hold open). Other coasters on park consistently exceed 1,000pph; the likes of Nemesis and Galactica are always over 1,000pph by a fair bit, Thirteen mostly is, and even Wicker Man often gets a solid 1,050pph.
And another thing to add is FT/RAP, and how that impacts the main queue. With Smiler being a popular ride, I’d imagine that like Wicker Man, its FT/RAP demand is quite high. Unlike Wicker Man, however, the throughput is often much lower, so that will naturally eat into the main queue throughput more and make the main queue longer. I’d imagine Smiler’s main queue throughput could well be one of the lowest main queue throughputs on park when you combine the low-ish base capacity and the high FT/RAP demand.
I won’t deny that it is a popular ride, but I think other factors need to be considered when deducing the cause of its relatively long queue time rather than just automatically assuming that “everyone goes there first”.