So, how would u suggest to use it?
Stuart is not a shock unit so don't use it that way. As Jar mentioned it, it does the job to cover your flanks from lone capping squad so that's one task you can assign him. Otherwise it needs combined arms to perform decently, the sight range increase at vet1 and gives quite a boost for a faction lacking sight if you hadn't selected a dedicated doctrine with sight bonus, M20 + Stuart combo can also be quite a thing early game to roam the battlefield.
The main function of the stuart is to offer support to your squads, you say zooks are better to keep lvs at bay but I'll answer that zook + stuart can seal the deal vs any lvs.
Following that logic the stuart is not difficult to hit vet2 or vet3 when your first medium hit the field, it is then up to you to swap crews...
I have to recognized that unlike I thought at the beginning I'm mostly using capt that lt since the patch went live but that's because it feet better my playstyle than being better than T1.