Prism
Explorer
You make a good point. But to me this feels like it slightly invalidates the class needlessly, in that the spells are intended to augment the Eldritch Knight. Why restrict spell-use or weapon/armor choices "downward" (if you get my drift)?
I have an Eldritch Knight in the party and the player was non-plussed that she couldn't use a shield. I don't see much of a problem letting her have both, so I am tempted to waive the somatic component for that class given how few spells they have.
On the other, tactical class trade-offs are interesting in my opinion (not necessarily my player's opinion). However, in the negative scenario indicated, it suggests that it is less of a tactical option and more of an imposition.
I play fighter spellcaster...actually a fighter/wizard but the same problem as the Eldritch Knight. He uses a two handed sword so I just assume manipulating between hands takes no real effort. Grab in one hand, cast a spell, grab with two - that kind of thing. If it wasn't that way there would be a few monsters too that would spend their time juggling weapons to cast spells which isn't exactly what the DM wants to be worrying about. I do tend to use the component pouch so I don't have to worry about holding wands and the like. Except for the fact it doesn't seem to be able to hold all my small glass beads without them falling out as others have noticed.
Using the same idea I cannot see a problem ruling that you can move a weapon to a shield hand while casting and then back again ready for combat. 3e had a light shield that let you do that specifically - no reason 5e can't assume the same. Holding two weapons in one hand seems fine too. Besides, if a DM gets to strict about it the player is probably going to work out that they can drop their weapon (freely), cast their spell and then pick the weapon back off the floor all by the rules. Deeply unheroic.
I reckon its only reaction spells and possibly bonus spells where I would consider the timings of swapping weapons/focus