Solitaire T costs twice as much, tiny difference is not worth doubling the price. Then you might just as well buy wired headphones to get even more out of it
The Solitaire T (ST) is costing double in the the USA ($800 vs $1600); here in Europe the Bathys costing 800 EUR and the ST 1300 EUR (not double price but about 60% more).
About a better choice being buying a wired-only headphone and not the ST, probably not true because people looking at the Bathys, iO-12 or ML 5909 are looking for a BT and/or ANC headphone. The ST, in difference with the Bathys, is offering a truly full passive (wired-only) mode, an excellent wired-only headphone with VERY good ANC performance, the
only ANC headphone, by the way, that is offering a really very close tonal balance between between wired-only and BT modes (the Bathys and several others ANC headphones don't offering wired-only option).
In wired-only mode, several ST owners, with experience of others wired-only (very) expensive headphones, reporting that the performance is excellent, like a very good wired-only headphone that don't have BT or ANC capabilities (I personally using my ST for one year primarily in BT mode). T+A (manufacturer of the ST) first designing the ST like a very good wired-only headphone and then they adding the BT and ANC aspects -- and one of the two ST BT modes, "Hight Quality" mode, is unique in its tech to all BT and ANC headphones, with truly excellent sound.
So, the ST is, in fact, a great 2 in 1 headphone, and in that case maybe not so (extremely) expensive like some people thinking. Several ST owners using the only-wired mode (3.5mm single ended or 4.4mm balanced) more than the BT and ANC modes, this last modes they using for travelling or similar occasions.
(** After one year I selling my ST and buying the iO-12 and deciding keeping the iO-12 for reasons that are very personal for me. The ST and iO-12, in my view, are the best two sounding ANC headphones in the market today [and I owning the Bathys, ML 5909, H95, PX8, AirPods Max and several others expensive ANC headphones] **)