In many ways, the Raynor/Titan combo is a refinement of the Hecate/Orion combo of earlier times; while there probably are no new Orions being built, they would only be decommissioned when the replacement has finished its acceptance trials. Also note that decommissioning does not mean "sent to the breakers", mothballing them is a much more likely thing for the GTVA to do (after all, the Orion has some sentimental value attached to it, and unlike the Battleships of WW2, their combat role hasn't disappeared).
Absolutely. Especially with regards to the Titan, I've always had the impression that the next gen destroyers were all about combining the best of the Orion and Hecate designs and taking lessons learned into account. Were it not for the threat of dozens of Sathanas juggernauts overshadowing the threat posed by any other Shivan fleet composition, even the Raynor would be an excellent next-gen line combatant and brawler.
And the Orion class is just...man, I imagine even the Vasudans would have a lot of sentimental attachment to the Orion. Between the Galatea, Bastion (both in Great War and Second Incursion), Nereid, Carthage, and Orions that brought down the Hades, they've helped the Vasudans a lot more than anything the class did during the T-V War. Hell, the Galatea's final mission was a desperate stand against the Eva and Lucifer to buy time for Vasuda Prime's evacuation (and it succeeded in destroying the Eva, to boot); the Bastion protected refugee convoys from Vasuda Prime after it was glassed by the Lucifer, destroyed another Demon, and ultimately saved the Alliance when it brought the Lucifer down. Then it sacrificed itself to seal the nodes from Capella (along with the Nereid). Oh, and the Bastion's pursuit of the Lucifer had a number of Vasudan wings operate from the Bastion as well, which is all kinds of interesting. Makes me wish there were more custcenes with Vasudan and Terran pilots in the same briefing room.
The fact that it still actively serves as a frontline destroyer class (even if heavily modified), at least 66 years after its debut, is just awesome.
Definitely a good idea, but the GTVA's failure to do so back during A Flaming Sword militates against it.
In general we are going to cherrypick canon information to make meson fireships useful in specific strategies but not a great general-purpose kaboom option. If the Tevs pull off a meson surprise it'll be because Steele figured out something clever. 
Does this imply that there are ALREADY meson fireships to be used by the GTVA in WiH2? 
And ninja'd
Sorry, but what exactly is meant by 'meson fireships'? Are we talking about large ships stuffed with Meson warheads for node-sealing purposes, or a ship that utilizes meson bombs (...or just meson beams? Confused...) as a primary armament?
If the former, well, I'd imagine the GTVA would place a heavy premium on that stuff. If the Shivans have potentially endless numbers, the only lasting, effective counter is sealing off nodes that Shivans do (or might) come from. And its probably a tactic that the Shivans wouldn't be driven to 'humanity and zods need to be exterminated' mentalities over (after all, nothing quite says "We really aren't some aggressive, destroying empire" like sealing off nodes to new systems that you might try to conquer).
