Is this arrangement (D, N, T, L, S) of the sounds intentional? Had someone explained this to me regarding point of articulation and DeNTaLS when I first started learning Irish, I would have smacked myself in the head.

It is arbitrary, and a little misleading, but it is easy to remember.

In Learning Irish, Mícheál Ó Siadhail merely says t and d resist lenition. In fact they resist both lenition _and_ eclipsis, especially after n (which he does say indirectly elsewhere).

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

Only saw this now, indeed, it is valid in all the Munster dialects, d and t are always eclipsed whenever the other letters would be.

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The dialect I use is Cork Irish.
Ar sgáth a chéile a mhairid na daoine, lag agus láidir, uasal is íseal