In that case:
You never really need to cap a point. If your fleet is superior, it will end up taking those points anyways unless your entire fleet is nothing but slow ships. If it is inferior, it will end up losing those points anyways. There's barely any middle ground and if you have the skills which does the same thing, the effects of them are minimal in comparison.
The best ships for harrass and assist in PD is just another big ship you can build like your Conquest, Astral, Legion, Odyssey or Cruisers like Doom, Eagle, Falcon, Heron. They can be their own PD. All carriers are essentially range 4000 PD or harrass depending on configuration, with the bonus that they are replenishable in a way that frigates and destroyers are not. Though I suppose it would be the carriers that need the support. I guess Omen and Tempest and telling it to escort can be useful too. There's no real need to use them though, unless you happen to have less than 20 DP to use.
Actually that would make an interesting discussion. Which would be better? 6 Conquests, or 5 Conquests, each with a Tempest Escort? What about omens as escort? Orders?
because in the later stage of this game, it feel more like a RTS game, the safe and boring way is carrier spam, at least AI carrier can do a decent job, if their number is up to some level, they can take care of anything, I guess I am looking for other option mostly because I don't like using carrier myself and would like see less carrier in my fleet. 
Don't use carriers if you don't want to use carriers then. I've played fleets without a single carrier. The rest of the post is still completely valid. In theory an Omen (or perhaps even a shade!) would be great PD, but the best PD is really just another cruiser or capital ship as a threat that can be retreated behind and has it's own innate PD. I'm not really sure why you need PD anyways. In vanilla starsector, hardly any opposing fleets will use proper bombers, so a pure combat ship fleet will never encounter any real problems against carriers. Some pather and pirate fleets might use lots of missiles, but since most of those are short ranged strike missiles, a dedicated escort frigate is of limited value. I do suppose that a frigate or destroyer can be used to escort a capital with a vulnerable rear, but that's not PD defence and more of just straight up killing any other frigate that may circle round the rear if otherwise isolated. I find that other cruisers and capitals do a good enough job of escorting each other to protect each other's rear in that respect. If you are using "harrass" in the RTS context, there is no economy to harrass and so no need for harrass.
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Churning out disposable frigates with elite hullmods is pretty good support even late-game. Just expect to lose some.
What decides what is disposable? Money lost will always be money lost. Wouldn't it be better to just simply not lose ships for greater gain by producing ships that kill faster and lose nothing in return?
