Not at all. You'll find very quickly that those
LRBTs:
- are very imposing, making them seem like a threat
- don't kill very much (unless you go hot)
So they should provide you with a decent 500 point game, even against newer codexes, unless your opponents go all-in with meta units/lists at 500 points. (e.g. lots of 3 wound marines)
The guard squads are pretty much screening units, as they struggle against even T3 bodies. The worst thing is if both your tanks get tagged in melee, so try to keep the tanks a ways apart (like 15"), but within
LOS of one another, and the guard squads between your tanks and your opponents (we call this bubble wrapping). That way if/when one tank gets tagged in melee, it can back out of combat and the other can clear whatever tagged the 1st tank.
HWTs and
LRBTs are in the same boat, they're kinda expensive, and are lacking output, but the
HWTs are also highly vulnerable to every weapon in the game.
LRBTs are vulnerable to higher strength+
AP weapons, but there are usually less of high-S&
AP in smaller games. So if you can protect your tanks (and not over-expose them and properly screen them with the infantry squads) they'll live a little longer.
If your opponents have a lot of regular marines and intercessors (2W models, not 3W gravis), then it's worth trying the
HWTs. For 150 points, that's 3
HWTs with heavy bolters, and those can do some work. At higher points levels, opponents have the points and units to deal with both tanks and
HWTs, so they're not worth it. But at lower points,
HWTs can fill a niche, and are still fluffy and fun to play (though movement is a problem...)
If your opponent(s) are going with meta lists, then there are several things to try (but play the list as-is a few times just to get the feel of it)
- Take the relic Cadian Battle Cannon from War Zone Octarius (it's absolutely unholy) instead of the Eradicator. The Strength 8 and flat 3 damage does wonders.
- drop a company commander (you don't really need 2, but to start it's good practice for orders) and upgrade a
LRBT to a Tank Commander.
- drop the 2nd
LRBT for a Full Payload manticore. Again, the damage 3 does a lot of work.
You can go with a Demo Cannon on the tanks, but the 5 point cost makes for a weird points total. Since you're exactly 500 points, I'd go with the relic battle cannon for the consistent output.
Just be aware, going to the Tank Commander and Manticore is a full-meta list, and is extremely oppressive at 500 points (and still

at 1000). So make sure that if you're going with oppressive units it's because you're playing your army correctly but are still struggling to compete, not because you want to be *that guy*.
This should get you familiar with the army and how it plays while building your confidence, and give everyone a bunch of fun games :-)
p.s. remember the sergeants on those squads can take chainswords for 0 points and get that extra attack