Re-Doing Spell Durations: Magic-User

I've been looking at simplifying and unifying spell statistics for Liber Zero, again, mainly because I saw a forum thread wishing for more "build your own" rules for monsters, classes, and spells, instead of lists of those things. The last official post I did on this was the revised spell statistics post, although I did massage these a bit when I did my spell study series and stripped them way down when I proposed a cheap, tiny version of D&D.

I was looking specifically at the spell durations, first. For magic-users, I had come up with:

Instant: open-ended change of state

Brief: turns = spell level, minimum 2 turns

Standard: 6 turns/2 spell levels

• plus caster level, if physical
• or 2d6 turns, if combat-related

Every spell type would be considered Instant, Brief, or Standard. But I'm wondering what the harm would be to merge and compress Brief and Standard to just "2d6 turns/2 spell levels, half that for spells that delay or interrupt, with a bonus = caster level for physical effects like flight or levitation".

Reasons in favor:

1. Many combat spells are already 2d6 turns.
2. Since many low-level non-combat spells are 6 turns, replacing the duration with an average roll of 7 won't be too bad.
3. We give physical effects a level-based bonus, just so players can predict how long Fly might last.

Is it really so wrong?