Spellsword is a very competent martial and spell-caster, it currently has a good kit and spell list.
Mordenkainen's Disjunction is a very oppressive spell, and one of the reasons it was kept in check was because it was only available for wizards and sorcerers wich have their own weaknesses, having Mordenkainen's Disjunction on a very strong martial that can also access ESF:Abjuration makes the spell too strong in the hands of spellswords, as they can quickly and easily strip wards from a large plethora of different characters and even being a standard 27/3 caster that is 29CL against dispels wont provide a good enough safety net to resist the power of double Mordenkainen's Disjunction with ESF:Abjuration.
The thing is, Spellsword kit is already very good without Mordenkainen's Disjunction, it has Elemental Strikes, Imbues, Maelstrom, Spellbook Faerie Fire, a very good attack progression 0/-5/-10/0 instead of 0/-5/-10/-15, CL30 haste, etc. It certaintly doesnt needs Mordenkainen's Disjunction to perform excellently both in pve content and in pvp encounters.
This would add a good layer of strategic decision for spellswords, as they also have greater dispel and greater breach in their spell list (wich are basically never used after they acquire mords) they would have to decide wich one they should slot in preparation for future encounters, separating the good spellswords from the great spellswords.