There's nothing wrong with that mechanism for character development, but personally I prefer ours, where soldier stats grow based on their actions during battle.
When faced with a choice like this, I generally prefer a mechanism which encourages the sense that a player's actions in battle or during the campaign (research, construction) have a direct effect on each other. If we give the player the stat points to assign in whatever way he wants, I think we would turn character development into a strategic choice, rather than something that emerges out of the decisions the player actually makes in the tactical game.
There are pros and cons to both mechanisms, but IMHO what made the original X-Com so good was how much the player's actions in the short game (battlescape) effected the long game (geoscape) -- and vice-versa. For that reason, I generally prefer systems which keep this interaction as direct as possible.