Have you considered Deathwing as a counts-as army list? Terminators would be a lot tougher for representing MI, and teleporting in would represent high-altitude drops.

Review Thoughts

Small tactical formations proved too vulnerable.
I am not keen to take them with Rhinos since that moves against the Starship Trooper theme.
Just could not get enough units onto objectives to claim a win.
Really not enough fire power to deal with war-engines or many armoured vehicles really.
A Heinlein cap trooper should be able to take on a squadron of tanks, . . .
Counts as Land Speeder was a useful device for cap troopers, on the bounce, but hard to get them into cover.

Have you considered Deathwing as a counts-as army list? Terminators would be a lot tougher for representing MI,
and teleporting in would represent high-altitude drops.

It feels odd to have a single tac marine per stand but a single termie per stand would fly a lot better in terms of stats.

In terms of the list, I would have thrown the characters into the Tac formations before the Speeders and relied on the Speeders just for support while the Tacs engaged. Swapping out some of the Tacs for Devs/Assaults would lend you a little more utility too.

RG are going to have issues against heavy WE/AV armies, yes. Crossfire with Speeders and supported assaults are pretty much it as you don't have access to Preds/Land Raiders.

We can ill afford another Klendathu.

You almost need to proxy them as Knights. Don't know how they'd fare without supporting artillery/normal infantry, But the speed, fire power and toughness of the individual units seem most similar. Unfortunately nothing by way of aerospace either...