I'm not sure what you've done with rexlar actually makes use of his ability. Since he is the centerpiece of your squad, you'll probably want to maximize his potential and fill in the rest afterwards. You'll want to throw as many dice as he possibly can, with as many mods as possible, while still having a focus to turn those damage cards face up. VI works well enough to get him to PS10 and try and kill someone before they even have a chance to activate that round, so it's certainly a good option. Another good choice is Expertise, ensuring that you won't need to spend your focus offensively and can save it for his pilot ability. As for throwing dice, HLC is expensive and doesn't work with the TIE/D title, but gives him the most bang for his buck. You're basically trading the potential of an ion or stress token for the chance of a critical damage. A cheaper option, but one that also doesn't necessarily go with the title, is linked battery. With expertise and a predator-esque re-roll, you will largely never need a target lock action, can save your focus to activate his ability and while it has a lower maximum damage than HLC, it has more consistent damage output. He also works well with 4 attack die missiles, but he might be getting too heavy at that point and you'll want to fill out the squad with more rounded ships.

With either of those builds (TIE mk. II, Expertise, Linked or HLC), you are getting easy means to lose stress, shooting at a modest PS 8, throwing 3 dice with a free soft re-roll or 4 dice without, have the focus effect and are free to use any action on your turn based on your target. If you're shooting at someone with 2+ shields, you're getting more returns from a target lock (particularly with HLC) but less than 2 shields and a focus will help you push through those crit cards. You're more prone to barrel roll with the Linked battery build, at least early on, and you won't necessarily need a targeting sync (although it is very strong with an HLC). You can actually fit in QD with LWF, Spec Ops, Adaptability, FCS and TS if you want to use her as a means to really set up Rex to lay down the hurt. That only leaves you 15-20 points based on build to fill out with a third ship however, so a lighter TS carrier wouldn't be bad.

Ultimately, Rexlar is overpriced for what he brings, but he can certainly be fun in a less competitive setting. If you're just looking for a jammer, I'd stick with Vessery or a Glaive.

Oh, I should have mentioned: I'm not using Rexlar for the ability, just for the PS to get a Jammming Beam shot in for OA's Opportunist.

What are you cutting to fit in Opportunist? You could also just as easily give him Swarm Leader and run more /fo's. Throws more dice, cheaper and no stress. Jamming Beam is also a lot more effective when you have a second form of control, either a way to give stress or ion tokens. You not only have to remove his tokens, but also limit his ability to generate future tokens and target locks to keep opportunist active and neutralize his modifications. It sounds like what you might really be after is a way to grant extra actions to Omega Ace to ensure he can safely throw 3-5 crits each round. You might be better off with a ship with coordinate or squad leader, rather than trying to force the jamming beam.

Yeah not seeing your list here. The Synergies and not working at all. Rexlar wants a higher or equal PS to strip shileds first usually if you’re using him as a staple. OA, needs ways to easily increase his threat without drawing fire. So Paired with Quickdraw with a Targeting Syncronizer or the like. OA opportunist doesn’t need a beam he needs threats in front of him that forces tokens to be spent and shields to be used ideally.

Rex can work - you use a 37 point Juke rexler alongside HotShot Copilot RAC.

But you don't focus on getting Rex's ability to work, you just use him as a high PS gun.

And there are way better options which are less predictable, now.

The key to Rexler (my favourite pilot by far) is to take him for his high native PS and not for his ability which, while fun, is a 'planets aligning' kind of deal.
That said, my all-time favourite build for him is TIE x/7, Expertise, Twin Ion MkII - which gives him the highest liklihood of using said abiltiy as well as being very action-efficient. 40pts isn't cheap, but its cheaper than trying to build him as a TIE/D (which, really, no one besides Vessery should bother doing) and far more likely to have an impact on the game.