I may be even more off base here, but I spent a fair bit of time with the dsl command pipe, and the piped commands to the modem chipset are not filtered, you can push all sorts of commands, even bogus, down the pipe. "Setting RA_MODE" means sending a "g997racs" (G997_RateAdaptationConfigSet) down the pipe. If a parameter of "4" is not accepted, it's the modem firmware that rejects it, not the driver that filters it.
If it works for you, great. It also works just fine on my SOHO line (VDSL2, no vectoring, DSL from the FTTB termination in the basement.)
However, my home line is a different story. As much as I wanted to keep everything all-in-one, with an XRX200 my DSL line (both on VDSL+Vectoring and previously on ADSL2+) always started out great with an SNR of around 12dB, then kept gradually degrading over the next about 7 to 14 days to the point where the SNR dipped way below 4dB and eventually resynchronized.
I then recently switched to a Broadcom based modem (the rather affordable ZyXEL VMG1312) and never looked back. The Broadcom modem manages to recover all dips and keep the line rock stable, my SNR curve now looks like a calm lake with barely any ripples:
The only downside with this particular modem is that the VMG1312 only has 100 mbit ethernet interfaces. In effect this means that I "only" get around 98 mbit out of a line that can, theoretically, go to about 112. But in practice this hardly matters, and I will gladly exchange a few mbits for the stability. And in the process I switched the router to something that speaks 802.11ac, which is a definite improvement over the Lantiq modem routers that (with the exception of the HH5A) only speak 801.22n.
For the longest time I thought that the modem chipset does not matter as long as the line is fine. I was proven wrong, and I now regret that I didn't try Broadcom much, much earlier. In fact, I am very much tempted to switch the SOHO line to a Broadcom modem, too.