(When) Can I use Cat5e wiring to carry a POTS signal to a DSL modem?
During my conversation with Jack Creasey, I “refreshed” in memory some normative material on ADSL and think that the next could be interesting:


Source: ITU-T G.992.1 (06/1999), ADSL.

Along with small guidelines and useful limitations, it could be considered “indirect evidence” that CAT5 cable is at least assumed as a possible in-home wiring by the then-days researchers.
Moreover, ITU-T G.996.1 (02/2001), Test procedures for DSL transceivers, considers CAT3 (predecessor?) cable appropriate among in-home wiring models (see subsection 6.2).
Maybe, this will give you additional confidence around your cat.5e cabling.
P.S. Also, Annex A/G.996.1 describes the characteristics (from 1 Hz to 5 MHz) of 26 AWG, 24 AWG, and 22 AWG cables (and test line models based on them) which are used in (lab) performance testing of G.992.1 ADSLs. Who knows, may be modern Cat. 5e fits the then-expected requirements...