I wondered if the “pounding” was considered of poor taste only by Seámus Ennis, or if it’s wider view.
Now I listened to a clip of Liam Walsh where he does it - http://www.archive.org/details/LiamWalshTheNewDesmne - and it reminds me of the piano accompaniment of that time - it gives nice beat, methinks. So why would it be bad? I don’t mean I’d do it all the time (and regulators are at least 5-10 years away from me 
), but for example here, it sounds rather nice I’d say.
For me personally there’s no hard fast rule. I just think of regs as I would any other accompaniment, whether it be piano, guitar or bodhran. If it adds to the music then that’s great if it distracts, overpowers or tries to drive the music then it’s too much.
I’ve read that Ennis didn’t like Leo Rowsome’s regulator playing. LR influenced many pipers - was Liam Walsh one of his students? Some of Liam O’Flynn’s early solo recordings have a distinct Rowsome sound to them because of the style of regulator accompaniment.
LR’s regulator playing didn’t vary much. He tended to stick with the same (down beat) rhythm all the way through a tune.
Ennis, on the other hand, varied both the rhythm and chords played (and sometimes simply did not play regulators). Ennis would also lean on the regs, playing 3 key chords for long periods.
I’m listening to Johnny Doran’s recordings at the moment. He played regulators almost constantly, but had tremendous variation in what he played, both on an off the beat and using all sorts of chords.
Ee, Liam Walsh was a pupil of Willie Rowsome - but the similar style of playing makes sense this way as well.
Hm, I hear about those Liam O’Flynn early records all the time, yet never found any - don’t you have a clue how to get them?
Leo Rowsome played long chords as well…but his playing was different, of course, than that of Seámus Ennis. But I like them both…
Regulators are difficult beasts - sometimes they are really great (Mikie Smyth, for example), and sometimes, nothing much would happen, if they were not present. And there are many different ways of playing them as well.
Johnny Doran’s regulator playing is great - and time has been merciful to The Bunch of Keys, the regulators aren’t overpowering. And with the “travelling style”, it helps the articulation. I just wonder how more closed-style pipers (like Tommy Reck) would sound with such accompaniment.
The clip I heard was on an RTE webcast - probably the Rolling Wave. Have a look through its archives.