Yes, but whereas your 'what-ifs' are baseless and have no relevence, the fact that it's the entity (really, i've only used this line...once?) that sent Marle to the DBT makes sense because it's needed to occur so that Crono continues the quest.
Crono & Co. obviously have superhuman powers of strength along w/magical ability, which they show throughout the game, heck, just take the various giant jumps they take: from the Epoch onto the Black Omen & from Mystic Mountain's gate. I don't think that them being able to deflect bullets from archaic guns (which Lucca herself probably helped create) would be a terrible stretch.
And now it looks like you're trading in 'what-ifs' for 'should haves'
The Entity wouldn't be stupid to leave them w/powers? Since when does the Entity control such things? What shows of power do we know, from in-game evidence? Time manipulation. That's more or less it.
Of course Magic faded over time in the Zealian bloodline because they stopped using it and they also mixed w/the Earthbounds. It's not like Magic just dried up overnight.
It was Lynx, the powerful foe who's part man, part beast, and part machine, Harle, who's the 7th dragon, lots of fiery monsters, a flaming orphanage, and, of course, all the kids to protect. Lucca was outnumbered, outgunned, and outmanuvered. There was too much going on for her to worry about.
Anyone who said Leena is Crono's daughter is on drugs. Plus, no where in-game, again, a helpful phrase, does it say that Magic is enheritable. You still need to unlock it as far as we know.
You paint a picture as if it's just Crono versus hundreds of Porrean soldiers. Crono & Marle would be enough, with her support abilities Haste & Cure. But then, you've also got the (largest?) army of Guardia behind them as well. Perhaps Porre was building up resources in those 5 years or so...but think about it, their leader was simply the Porrean Elder...not even a King...
Not to mention there's that stuff about how Guardia rebounded...