The way I see it, when you give a character the order to attack, you are ordering the character to attack for one turn, not for eternity. Hence, it makes sense that you should be prompted to choose an action for the character on that character's next turn. Also, the interface doesn't overly favor making an attack over casting a spell, the way some games do (including Ultima 7).
(Of course, there is still the problem of spells needing reagents, which tends to discourage the use of weaker spells like Magic Missile/Arrow.)
Also, in my experience, other creatures taking turns outside of combat doesn't really slow down the game unless actual combat is taking place. Plus, that issue is really only for Ultima 6; in 3 through 5, you normally don't have this happen, except for the rare creature that can attack outside of combat.
Turn based systems are best when you have a lot of options and tactical approaches to combat. There are many ways they could have improved on a turn based system, but since they chose to do none of these, they were right to eliminate it entirely. There's simply no good reason why anyone should have to micromanage every swing of Geoffrey's sword or every step he took on the way over to the enemy.
I can't recall ever having a lack of reagents, except back when mandrake root and nightshade had to be harvested. They've always been cheap and available in bulk. Ultimas 6 and 7 throw so much gold at you anyway that you'd be more likely to run out of mana before reagents.
It wasn't noticeable in the earliest games because you controlled one character (at least on the map) and spawn rates were low. When Ultima 6 and its spinoffs upped the number of spawns considerably, it became a real issue. It had nothing to do with actual attacks, but rather the fact that everything had to take its turn just to move, even if it was peaceful or couldn't see you. Merely being nearby slowed down the gameplay for no legitimate reason. If U7 had continued to run on that same turn based engine it would have been an objectively worse game for it.
Actually, there are tactical options. In particular, there are spells you can cast during combat (for example, to attack or to heal), and there are items you can use as well. Also, why is Geoffrey using a sword rather than a bow or a morningstar? (Geoffrey actually isn't the best example; consider Mariah, who has a lot of spells to choose from, or the Avatar, who is the only good spellcaster in 6 (why isn't Jaana a mage?) and the only spellcaster period in 7.)
Also, real-time combat is less accessible than turn based combat. People with bad reflexes, or those that do not have full use of their hands, have far more trouble with real-time combat than turn-based combat.
The reagent issue comes from the fact that:
1. You have to go out of your way to purchase reagents, especially with no shop selling them all. Also, enemies don't drop them, so you can't just accumulate reagents without going out of your way.
2. Using spells uses up a consumable. It doesn't matter how common the consumable items are; there is a psychological effect that makes many players (like myself) rather hesitant to use them, which goes against the fact that players should be given more tactical options.
The games would be better if:
1. All reagents except mandrake root were removed from the game entirely.
2. Any spell requiring mandrake still requires it, while all other spells require no reagents.
That way, there would be less micro-management of reagents needed, and mandrake could still serve as a limiting factor for spells that are strong enough to warrant it. Meanwhile, using a spell like Magic Missile/Arrow as a character's main attack becomes a viable option, with spells like Explosion and Mass Death being saved for special occasions.
Note that this is looking something like the Might and Magic approach, where some spells require gems to cast.