The Str 8 handles everything your talking about, points cost or no.
Well gee, a squadron of Russes would handle all of it as well, it doesn't mean it's efficient or good.
With a Farseer and Perfect Timing
So a 100pt model rolling 3 times for a 1-in-6 chance, attached to an 8 man unit costing 300pts plus Exarch plus toys, plus any fortifications you might have bought for them to camp in? Reliable? No. Points effective? Hell no.
or a Tau Commander and a Sensor Suite you can kill Quad guns and their like without any resistance
More reliable than the Farseer, but 105pts (assuming no other systems or weapons) and requires you to ally in Tau.
most other AA options are AV 10 or AV 11 meaning Str 8 will punch through it.
What other AA options? How many are going to be in range and LoS of the Reapers? How many of your Reapers are going to be alive?
Even other Flyers will get hit simply by twin linking the weapons again with a Farseer or a Commander.
Only if you have a large unit of Reapers. A unit of 3 only inflicts a single hit on average when Twin Linked, so a unit of 6 averages two hits or so, with negligible AP values against AV12/11 vehicles with 2-4 HPs.
Its 38 points sure, but its 38 points that is going to be very versatile and can win you games.
If your opponent can't handle >10 models that cost over 400pts for T3 and a 3+ for protection, they're shit opponents. Sorry.
Only certain units like a Riptide are a problem, and that's mostly because of the JsJ rather than the 2+ armor.
Are you joking? 10 S8 shots nets you 7 hits without twin linking, 6 wounds, and 1 failed save. A Riptide can tank that shit all day in the open while blasting back with BS5 cover ignoring pie plates of AP2 death. And that's only a 185pt model versus your 300pts.
Going second 50% of the time is not quite right. Among other things you can alter your rolls to see who goes first or seizes, you can (as an eldar player) have a 2+ to seize if you really want too. If you are worried about going first one Selection of Void Shields can protect any flyers who enter their territory or you can fly them behind LOS blocking terrain or behind terrain that provides a nice save like a Ruin or a Landing Pad.
If you spend even MORE points just to alter that dice roll, or ally in even more armies completely unrelated. Void Shields apply IF you're playing Escalation (I don't know anyone who does, certainly most tournaments won't). Ruins are certainly a useful thing to be behind, but you can't always guarantee there will be some on the table tall enough to matter, you're sacrificing your own fire arcs to do so, and restricting your own movement phases.
Really you have a lot of options, but worrying over one T7 2W model or one Stalker, or a TAC squad with Flakk shouldn't prevent you from taking some Hunters as Dark Reapers handle nearly everything. Heck with Tank Hunters you can even bring down a AV 14 building fairly reliably with 9-11 Krak Missiles (twin linking of course)
If a unit that statistically loses a near 40pt model for roughly every 6 boltguns that are fired at it (not even 6 hits, 6 SHOTS) is handling "nearly everything" then you really need to get out and play more opponents. Like, really. They don't even have Interceptor, so the first Heldrake you come across is going to wipe 75% of your unit out on the first pass.
Bear in mind that all of this is in defence of a 160pt Flyer with AV10 and 2HP that only puts out 4 S8 AP2 shots. You can take a Falcon with a Bright Lance (one of the most choices in the codex) for cheaper, it shoots from T1, and has a 3+ save behind a ruin or 4+ in the open, AV12 and 3HP, and can transport a scoring unit. You can take Hornets from FW that have paired Pulse Lasers for sub-100pts per model in squadrons.