No, I included multi-class feats (which do not increase defence, and rarely increase damage) in my disagreement with the line of yours that I quoted in my post, which specifically referred only to "eliminating all damage and defence increases from feats, you almost entirely eradicate the optimisation issue from the game".
Nor did I make any claims that any combo was overpowered. Merely that optimization is more than just taking the right feats.
It doesn't take any great insight to notice that there are some powers that are strictly better than their competition. Twin Strike is flat out better than Careful Attack in almost any situation. It is, on average, more likely to hit, and likely to do more average damage. It's more versatile, able to target one or two creatures. Selecting Careful Attack instead of Twin Strike is sub-optimal. Significantly so.
Compare a ranger build that uses entirely single-attack, standard action exploits to one that selects multi-attacks.
Multi-attack standard action powers are better than single-attack ones. Minor action attacks are (generally) better than standard action ones. Immediate reaction attacks are better than minor ones. Immediate interrupt, better still. Free action attacks? There's a reason they issued a rules update limiting those to once per turn.
There are Paragon Paths that are flat-out useless, mechanically. A player who selects purely on flavour can choose one that offers them no actual in-play benefits. There are others that give significant bonuses to damage, or defence, or durability. Choosing the right one impacts your character far more than any one feat ever can.
Compare magic items that offer daily powers vs items that offer properties, at will powers, and encounter powers. Compare the non-feat static damage boost of Iron Armbands of Power vs. the daily power (only triggered when you get critically hit) Shield of Defense. The gain in action economy of Acrobat Boots (allowing you to stand from prone as a minor action, at will) vs. Dwarven Greaves (once per day negate ONE instance of force movement against you).
Optimization doesn't stop at feats. Without selecting any feats at all, you can build two characters of the same class that are vastly different in terms of survival potential, damage output, and defence. Powers and items that manipulate the action economy make a larger impact than a feat that gives you +1 damage per tier.