Having just completed considerable study of this issue of Evan Ragland's pedigree I think I have a very tenable solution.

The Welsh ancestry of Evan Ragland Sr. of Virginia c.1656-1717 finds a good starting point in Gwilym ap Jankym Herbert (aka Gwillym or Gwilm ap Siencyn – often transliterated as William or Wm. Jenkin), as there is little controversy from there. Gwilym’s son Sir Thomas ap Gwyllym, Knt.. c.1360-1438 fathered the heir that was to begin the Raglan surname, Jevan (Evan) Thomas whose son came to live at Raglan Castle. c.1392-1438. Ref. 1, 2 [pg. 741], 3, 4 [pgs. 52-53 & 228], and 8.

Marriages play a critical role in the Raglan line. Sir William ap Thomas Herbert’s first wife was Elizabeth Bluet from whom came Raglan Castle.. Upon his death his daughter Elizabeth became the heir and was married by Charles Somerset, KG. and subsequently, upon Elizabeth’s death, became “Lord Herbert” of Raglan Castle. Ref. 2 [pg. 777, 1st para. of notes] & 3.

Here is where a lesser-known son of Thomas (or Tomas) ap Gwilm Herbert, brother to Sir William ap Thomas, comes into play as forefather of Evan Ragland Sr. of Virginia c.1656-1717. Evan [Jevan in some records] is not mentioned in the annals of his more famous brother and nephew, thus we have but little notice of him. He is shown as simply Evan (a son of Thomas) in the genealogical chart of the Herberts, Ref. 4 pg. 228; frame #244 of 268, and as Evan Thomas Herbert in Ref. 6 pg. 5 slide #25 of 164. His line is covered more completely in Ref. 7 pg. 1, where he is called Evan Thomas, ap Glim Herbert though he was a brother to William, and in Ref. 9 pg. 260 of 626 - footnotes ; this reference is correct. His son Robert came to live with William. More is found on the Herbert/Raglan linage in Ref. 8 slides 443 & 444 of 639 [Linage 22].

From the listed references we can be confident in the Relationships listed below - Thus.
Gwilm ab Siencyn [Herbert]; c.1325-1377
m. Gwenllian Vychan (Vaughn) c.1340-1440

Thomas ap Gwilm [Herbert]; c.1360-1438
m. Maud Morley c.1375-1438

(sir) William ap Thomas Kt [Herbert of Raglan Castle]
c.1390-1445 m. Widow Gwladys (Gam) Vaughn d.1454

Evan (Jevan) Thomas [Herbert] --Brother to William ap Thomas
c.1392-1417 m. Margaret Grant

Robert ap Jevan [Herbert-of Raglan] --Raised with William ap Thomas
c.1409-1469? m. Joan Lewrch [Clerke]
John Raglan c.1433-1526
m. Catherine Mathew

Robert Raglan c.1485-1565
m. Wenllian [Elnor-Elinor] Vachan [Vaughn] c.1464-1585

Sir John Raglan c.1523-1605
m. Elizabeth Courtney

Thomas Raglan c.1575-1648
m. _____ Wood

Thomas Ragland c.1628-1684
m. Jane Morgan c.1630-1728

Evan Raglan c.1656-1717
m. Susanna Pettus c.1654-1760

References:
1. Ancient Wales Studies – the HERBERT FAMILY PEDIGREE By Darrell Wolcott http://www.ancientwalesstudies.org/id40.html
2. Annals and Antiquities of Counties and County Founders of Wales - Thomas Nicholas (London); Vol. 2 https://archive.org/details/annalsantiquitie02nichuoft
3. William ap Thomas the son of Sir Thomas ap Gwyllym, Knt (d. 1438) and Maud Morley https://en.wikipedia.org/wiki/William_ap_Thomas
4. Wales and the wars of the Roses https://archive.org/details/cu31924028052441/mode/2up
5. Parish Register of St Peters, New Kent County, Virginia; https://archive..org/details/parishregisterof00stpe
6. Genealogy of the Ragland Families, [and others], Margaret Miriam Strong https://babel.hathitrust.org/cgi/pt?id=wu.89080570682&view=1up&seq=1&skin=2021
7. Glamorganshire Pedigrees From the mss. of Sir Isaac Heard, Knt., Garter King of Arms https://discover.library.wales/primo-explore/fulldisplay?docid=dedupmrg268726185&context=L&vid=44WHELF_NLW_NUI
8. Ancestors of Evelyn Wood Keeler w/o Willard Underhill Taylor by Josephine C. Frost, Brooklyn, N.Y. 1939 - Slides 443 & 444 of 639 (Linage 22) https://www.ancestry.com/imageviewer/collections/11741/images/dvm_GenMono001365-00002-1?pId=450
9. MISCELLANEA GENEALOGICA ET HERALDICA. VOL. 1. 1874. by JOSEPH J. HOWARD -- footnotes page 260 of 625 https://archive.org/details/miscellaneagene00howagoog/page/260/mode/1up