For 18 Perception, you will get a grand total of +24% Interrupt. For Bows and 1H weapons, that's 30-40 at most, and will give you an Interrupt score of 37.2 or 49.6. When Interrupt calculation is changed to additive, 18 Perception and Interrupting Blows will give you 41.7 (30) and 55.6 (40) Interrupt.
Interrupt results are affected by the hit chance, as well.
Dual wielding Stiletto Interrupt Barbarians with their Carnage AoE hit would be interesting as the extra interrupt is probably worth more than bonus damage on Carnage hits (due to them being low damage), but that's about the only case in the game where I can see it being useful - which is not a good attribute IMO.
Personally I think Interrupt would be better suited to Dexterity, and Accuracy brought back in. That would give Dex the extra oomph, and make designing a fast attacking low damage character really viable.
You're viewing them in isolation. You can stack deflection with shield and other bonuses though. If you can get in a comfortable range where certain enemies will only graze/miss you, this strikes me as preferable than having more HP. Since everything in PoE hits like a truck anyway, being able to dodge damage seems better than being able to better absorb it. It also gives you more leeway with armor, since you won't need as much DR to absorb damage. Of course this all depends on how the final values are tuned.
I am viewing them in isolation, because I am viewing them based on what they are worth per attribute point. In our attribute paper, Matt plotted that +1 Deflection is better than +2% Stamina from CON when your Deflection is 6 or more points higher than enemy accuracy, and CON is better if it is not. CON now gives +3% and PER/RES give +1, which means that unless you have absolute bullshit Deflection, CON will grant more survivability.
Stacking Deflection (and I mean stacking it) is not useful in this game, it just plain sucks. Monsters now deal less damage. Damage stacking is now additive. Crits deal less damage. Deflection (and Accuracy) are no longer as vital.