Ok, the removal of IC vs infantry occurred way back when Sotec was the AC and went through a whole raft of proposed changes because the Eldar was seen as OTT. Personally I am not bothered either way - the point is one of priorities in the game, and I am sure that a SM player would gladly lose his Terminators if it meant keeping his BTS titan

However IC
is needed to ensure the statistics are appropriate against titans.
The point about the restrictions of the FF arc is valid, it is almost impossible to put them into static positions and expect them to be usefull; few enemy would intentionally 'blunder' into arc and range of a Cobra

. However that is not how you get the best out of the unit. In the scenario I describe, the Eldar player out-activates the opponent, and only at that point does the Cobra get positioned to fire in the following turn. So the target will be in arc and range, but the Cobra's shooting is effectively restricted by having to double or march to get into position (unlike other formations). And 75cms with a subsequent 30cm shot does cover a lot of the table

On the statistics, The maths is very simple. At 2BP, you get a 5+ to hit on sustaining against a titan, or a 1/3 chance per dice, with an average of 3 TK damage per hit. As you get 1 dice per 2DC, this gives an average amount of damage equal to 50% of the Titan's starting DC.
(Or 1/3 * 3 * 1/2 * Titan DC). Two Cobras sustaining gives an average chance of destroying a full strength titan, but three Cobras gives some redundancy and mitigates against failed activations etc
With 3BP, the power is significantly increased.
- When doubling the average damage is 1/6 * 3 * 1/2;
or 1/4 the starting DC - When advancing it is the same as above,
or 1/2 the starting DC - However, when sustaining the maths becomes 1/2 * 3 * 1/2;
or - - - - 3/4 the starting DC.
Potentially with lucky dice, you could get 4 TK damage per hit which would kill the titan outright. And the odds of getting 12 damage from three hits is 1/27, or less than the odds of throwing double '6'.
This is why I am cautious about this boost.
That said, the key to this debate is in the tactics, or how you use the beast. Cobras have to be made to work for you. They provide an excellent 'fear' factor to any large titan which can be game winning by its self if it means that the titan does not get used properly. And you do need some luck especially in the strategy roll off where your Cobras are the first thing to activate and unleash their firepower.