I don’t tend to use the bottle cage and camelbak at the same time, unless its an all day ride. Sometimes its nice to leave the camelbak behind. 1L of water gets me round a short loop for am hour or so. I can carry everything I need but my pump with me
It is all about the girth
Some 1L bottles are the same diameter as other bike bottles (like most 750 and 500ml ones) like this one:
I use the MTB version of that specialized one as it looks ‘cooler’ was about £6 and somethign like 35g, the weight of some carbon ones:
It will only take standard diameter bottles (so not the 1L SIS one (SIS do a 900ishml one too which I thought was 1L), but the fully closed loop and generally good ‘bottle support’ means a full 1L bottle doesn’t fall out. Pretty much every bottle cage I’ve used is fine with 1L bottles, though apart from a side entry bontrager one they’ve all had a full loop around the bottle