What I recall of the Swordmage is...

Defender. This means:
- high HD,
- a mechanic which makes this PC a preferable target for at least one enemy, and
- some form of lockdown / battlefield control.

The latter was accomplished through melee spell-attack powers like Booming Blade and Lightning Lure, both of which have been ported to 5e as cantrips.

Teleports to enemy when the "preferable target" mechanic triggers. This means some new mechanic.

Arcane. This means spells, at least half-caster; spells attacks and DCs are based off Intelligence.


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IMHO Eldritch Knight is not a valid substitute: the Swordmage uses cantrips at high level, and a regular Fighter's Str-based attack x4 is going to eclipse that. So the Swordmage needs something else to keep up at higher levels, and it must be something compatible with using melee weapon attack cantrips.