I don't think it suggests that.

For context, the section in which the quote appears is titled Litriú na Nua-Ghaeilge roimh an gCaighdeán Oifigiúil. As such, the quote refers specifically to lenition in the recent pre-caighdeán period, but later than the Old or Middle Irish periods. As I've mentioned above, the use of h to indicate lenition goes back to the earliest Old Irish sources. Ahlqvist was not only aware of this, but discussed it in the preceding section.

As you say, the punctum seems to be universal in Gaelic revival texts. I agree that it is very common in texts from this period, but strictly speaking it is not universal. Examples of h do occur in texts from this period, typically where the cló gaelach was not used. If you'd like to take a look at the following example it will demonstrate this point. This is the first page of the initial volume of the newspaper An Gaodhal, dated 1881. You can see from the title, which is not in cló gaelach, that lenition is indicated using h, however, just below follows a discussion of lenition (which is referred to as aspiration), and as the examples are in the cló gaelach the punctum is used to indicate it.

You can actually see in some sources how specific the use of the cló gaelach was to text written in Irish. For example, if you look at texts like the letters of Peadar Ua Laoghaire, you'll see that he used cursive when writing English, but the cló gaelach for Irish. If you find an Irish text from this period written in any script other than the cló gaelach, however, you are more likely to find that h is used to indicate lenition. Examples of this occur in both roman script and ogham, however, because of the preference for the cló gaelach during the Gaelic revival period they are comparatively rare.

With all of that being said, it occurs to me that a simple rephrasing of the original question may resolve the issue. If we were instead to inquire "when did the use of the punctum become the more common method for representing lenition in Irish", I think the answer is probably some time during the 19th century.

Oh. I see. So the "h" for lenition was maintained outside of Gaelic lettering through the period of the revival.

Exactly. And, it just so happens that this kind of non-Gaelic lettering became particularly rare when writing Irish during this period, except in niche cases like ogham, telegraphy, and publication titles like that of an Gaodhal.