What a counter-productive design philosophy... creating more lances to counter lances. That is not good in my opinion. Quite bad actually.
Unneccessary.
Look, I will always advice to not tailor a fleet. I say : design an allround fleet that can face every fleet. Best at 1500pts standard size.
If that IN player does show up with his gothics & firestorms because he knew he was going to face Space Marines: pull out your Eldar and call him a git. Play Marine models as count as Eldar if necessary.
Tailoring should be discouraged. You are encouraging it.
"Marines now have lances, nothing stops me from taking more."
The only fleet that is lance heavy per nature is the AdMech fleet. But this is an elite/expensive fleet, outnumbered and flawed at boarding/h&r. Precisely what Marines excel at (rock-scissor-paper).
Imperial will go for a mix of weaponry, Chaos as well, Eldar are a threat to Marines, yes, but official Eldar are horrid to anyone, Orks do not have lances, Tyranids are mixed with few lances, Tau have below average lances (except your NEW Tau draft...

). (codex creep anyone???)
There is main difference between the prow bombardment and prow lance option : intervening blastmarkers. I'd rather have lances on the Strike Cruisers to be honest.
Also: it is the core of Marines to be low on lances.
The design philosophy of the S.O. is still bad, even toned down. Background tells us it is designed to counter Tyranids. You need batteries to do so.
Mind you: I would / could support a S.O. that had str.12 (or higher! 14-16!) port/starboard weapon batteries at 60cm and no lances.
edit:
Only the smallest of vessels would be permitted to act exclusively as gunships, with the larger strike cruisers and battlebarges remaining predominately as aids to invasion, ensuring the Space Marines would never present a threat to the Imperial navy proper. Inevitably, the wrangling over interpretation of a ship’s “primary role†leads to some Chapters possessing rather more versatile fleets than the Imperial Navy is entirely comfortable with.
Despite the last comment, the Dominion list, with lanced Strike Cruisers are a threat to the Imperial Navy. Being gunships and all.
When a Thunderhawk Annihilator comes in contact with an enemy ship’s base, they attack it like bombers as described for bombers on p.30 of the rulebook, even if they have used their resilience to remain in play. Once they complete their attack, they are removed normally. Thunderhawk Annihilators cannot be used as assault boats.
Does this mean they do not act like Ork Fighter-Bombers (d3 attacks instead of d6)? I am rather opposed to this. I see no real need for them anyway but they exist so could tolerate them.
Honor Guard
Expensive for a one time attack that can be braced.