Rings only get 1/10 as well despite the altar buff (which is even worse, since they cost twice as much on top of that).
The altar kadala legendary rate buff problem with boots/chest/rings has been documented pretty well if you go back through the bug reports. There’s at least a few threads with decently large sample sizes, e.g. this one: Kadala Altar Buff is Bugged/Broken - #52 by Ivan-1503
If you scroll through, between the OP and a few different comments there’s some 500-1000+ gamble sample sizes on different slots showing many slots getting the doubled rate to 20% but boots/chest/rings only getting 10% despite the altar buff.
For ring data specifically, in that thread if you scroll through, I reported 52 legendaries on 500 rings gambled and follz reported 83 legendaries on 840 rings gambles. Both pretty much bang on 10%, not 20%.