True, as long as the characters are single-classed. Multi classed characters might still be relatively low-level in terms of spellcasters, and for some classes the issues go beyond a single encounter (like the bard's abilities which have durations tracked per day, so while inspire courage might last the entire combat, it's useful for the bard to know how many rounds they have left at any given time).
In general, I agree that at higher levels, most effects will last the entire combat. It doesn't change the need for tracking, though. Or for some of the other features requested here, such as being able to select multiple targets and apply AoE spells like fireball easily and quickly. An interface that allows individual targets to be selected, then those targets rolling an appropriate save before damage is applied, is very useful -- particularly at higher levels when there are more of those effects and more minions with special abilities related to those effects.
In DMGenie, combatants could be selected individually or as a group (allies vs. enemies). A dropdown would then be activated so that the type of roll could be selected (any of the skills or saves, plus others like Grapple or Initiative (when starting a combat)). The tool would then make for roll for all affected creatures and a dialog would popup allowing the GM to roll (or enter) damage and apply the damage using either Full, Full (save for half), or Full (save negates). And Evasion and similar (like SR) would be taken care of for each individual creature. It was/is a hugely powerful feature that you might not appreciate without having used it!
Cheers!