Well, it depends what part of canon you’re at, and what amount of canon you accept.*  I’m still not entirely sure what my headcanon is w/ his current abilities, but even if you ignore all of canon after IWTV, he’s been a vampire 225 years so he’s stronger just through age if nothing else. 

He’s also one of the only vampires in canon who has never “gone to ground” (hiding/burying oneself in the ground for an extended period of time in a state of complete or semi-unconsciousness), even though he’s had very good reasons to ;A;

 Armand describes Louis’ lack of powers here in TVA: “…unable to read minds, or to levitate, or to spellbind others except inadvertently, which can be hilarious, an immortal with whom mortals fall in love.”

Just from IWTV and into the later books, yes, Louis is referred to as physically weaker than the other vampires, and he doesn’t exhibit any of the gifts that some other fledglings have in canon (like telepathy, telekinesis). This doesn’t mean he doesn’t have any of these now, but that he hasn’t really exercised them in canon. 

Lestat tells us in TVL: “I never revealed to him half my powers, and with reason, because he shrank in guilt and self-loathing from using even half of his own.”

But he’s still stronger and faster than a mortal. He’s also able to defend himself and kick a lot of ass, so to call him “really weak” is probably an overstatement. What he lacks physically he makes up for mentally, he’s strategic in the way he attacks when he does attack, and he can hold his own against much stronger and older vampires (he took out most of the Theatre des Vampires on his own in IWTV!)

Part of his weakness in comparison to the rest of the coven is the fact that he was Lestat’s 3rd fledgling in such a short period of time after Lestat’s 2nd fledgling (Nicolas). In Ricean vampire physiology, a maker needs to wait a good long while between making fledglings; too much frequency will make subsequent fledglings weaker than they could have been. Plus, even though Lestat had the blood of a much older and stronger vampire when he was turned, Lestat himself was only a decade into vampiring himself. It seems the vampiric spirit discourages the transfer of powers from young vampires to their fledglings. If anyone got the bulk of that power, it was Gabrielle, Lestat’s first.

There is also some speculation that the blood transfer needs to be exchanged more than once (how it was done w/ Louis) to ensure a stronger fledgling. Marius, for example, exchanged blood with his maker multiple times when he was turned.

*Spoilers under the cut.

Louis was upgraded in Merrick, and in PL, he can fly (the Cloud Gift). We don’t know if he has any others now. Maybe we’ll find out in PLROA! He has a significant role in it, according to AR.