I agree with you. This won't work in 3.5 at all, but could work for pathfinder.
As for making it work in pathfinder, since you brought up low levels; Full plate is not actually affordable with starting wealth at 1st level. For that matter, according to the wealth by level chart (only a guideline, true, but most DMs I've seen tend to skimp here in practice) full plate doesn't realistically become available until 3rd or 4th level. Similarly the absolute earliest you would expect to see NPCs with F plate is 3rd (they get 1,650 gp under the heroic progession, which is exactly the cost for MW full plate - not even enough for a dagger after that).
Since you brought up some really good points in our earlier discussion I got to thinking about enhancement bonuses. Perhaps they should give +2 to damage, but no bonus to hit. . . (and MW weapons would simply add +1 to damage). You pointed out that it might be too easy to hit monsters, but too hard to damage them. Tweaking magic weapons in that way might be a nice, neat fix. It also makes power attack less of a mandatory feat. I don't like when feats feel like taxes, rather than extra special abilities you can choose. If you simply always have to take a feat or suck, it's not really a choice, and that's sort of the whole point of feats. They are a guaranteed resource your character gets from levels (unlike loot) which allow for customization. If you have to take a feat to be viable, there's no choice, so that's no fun.
Making enhancement bonuses only add damage (and doubling that damage) solves the same problem of changing strength in that way. Quadratic scaling is better than linear scaling. Also, I'm sort of sick of all of the interesting enchantments getting trumped by the almost always superior +1. That bonus to hit is usually more valuable than anything else you could add, even before the small damage bonus that comes with it. now you choose between +2 physical damage or +d6 fire damage, for example. The draw for the enhancement will mostly be that it multiplies on a crit. I guess it's a little better for sundering, too, but then it will be harder to actually land the sunder, so that sort of balances out.
One last thing that occurred to me, since you got the juices flowing, is that the game pretty much universally favors weapons with high threat ranges over weapons with high multipliers. It does so in two ways: first, there is the simple math side of things: many small crits are good against many weak opponents or single tough opponents, while rare but large crits are usually wasted on hordes of weak monsters, even though they are good against single tough opponents. Also, since you don't choose when you get your critical hits, there is a greater chance for your crit to end up overkilling even a big tough monster if you have a scythe rather than a falchion. Assume you have to land 20 average hits on a dragon with either weapon to bring it down. On average, the falchion will cause double damage on 3 of those strikes and reduce the hits needed to kill it to 17 (or 18 if your last hit overkills it), but the scythe will cause quadruple damage on one of them. The scythe wastes some or all of the extra damage 3/20 times (so ir might take 18, 19, or even all 20 hits to kill it), but the falchion almost never wastes those crits.
The math just favors high threat range.
If that weren't bad enough, in pathfinder, they compound this problem by introducing a myriad of critical feats, which cause extra effects (usually status ailments) when you score a critical hit. There's no save, and no increased effect if the crit is large (let's not even talk about the fact that if you get a x4 crit, your target is likely dead, and the status effect wasted anyway). You simply get 3 times as many procs for these crit feats if you use high threat range weapons . . . and since there wasn't any advantage to using a big multiplier weapon anyway (aside from cup de graces), those weapons simply become second-rate.
This means that you end up with a series of strictly optimal or strictly sub-optimal choices. . . not really choices at all.
Where am I going with this? Well, with armor providing DR instead instead of avoidance, lumping damage together into one massive hit becomes the order of the day, so now big crits have a useful contribution to make, and I'm honestly not sure which type of weapon would come out on top. To me, that's an improvement. Now you get a legitimate choice: wear down tough mobs with a lot of small crits, which don't pack that much punch after armor, but cause crippling status effects, or swing away until you get that one lucky shot that makes the targets armor a joke, and might just end the fight out-right. Different styles, neither is flat-out better. I like that.