Quoting to lend my support to your side of the argument.
I've been looking at Invokers recently (as my wizard has MC into one and is thinking of picking up a power swap feat).
A lot of invoker zones do something on the enemy leaving the zone as well as the effect for staying in - this is how wizard zones should work.
Take the FS for instance - if you end your turn next to it you get ongoing 5 save ends, if you leave it you take D4+int
Cloud of daggers - if you stay in you grant CA, if you leave or enter you take the damage.
Choices regarding zones should be more than just "move to cancel the effect" as in most of the cases the move action doesn't cost the enemy anything (unless they are next to a fighter than can get a free attack on a shift).
I wanted to give you XP, but I apparently need to spread it around. I'm in complete and total agreement.
The problem with Flaming Sphere, as it is now, is that it's way too easy to evade. If the monster simply takes a move action each round (and who doesn't, if able?), then the Wizard's Daily has no effect, unless he chooses to use all of his actions sustaining it, moving it, and attacking with it again.
Imagine, for a moment, a level 1 Wizard using this power against an encounter full of kobolds. Hardly an uncommon scenario. The kobolds, with their minor-action shifts, would dance around the Flaming Sphere like it was a bonfire on the beach, and the hapless Wizard would be more likely to burn his allies than the enemy. It's not difficult to imagine combats where Flaming Sphere's end-of-turn damage never happens.
I find it hard to swallow that end-of-turn damage is "better" control than start-of-turn damage. But I can perhaps buy an argument that Flaming Sphere was too good, in need of balance. If this is the case, though, then the pendulum has swung too far in the other direction. The power now needs something, anything, to make it a contender. If it was too strong before, then it's definitely too weak now.