Warlocks aren’t inherently powerful. The strongest Warlocks in Warcraft lore have typically been aided or influenced by various demons. That’s sort of their thing
Siths in Star Wars are different in the sense that their power is entirely their own.
Warlocks drain life as energy from their opponents. A sith lord has a lot of energy, while most likely being more powerfull up front
So if it would be a time consuming battle warlocks would win. And its possible that it would be due warlocks being resilient, and protected by powerfull demons aswell as soulstone.
If I remember correctly, a vanilla swtor (yes, I used the term, meaning everything before KOTFE) Sith Inquistor is a councilmember with vast resources of the Sith Empire and has 5 of the most badass and resourceful companions. Khem Val alone could probably deal with any demon WoW Warlock could summon. If you meant more powerful warlock than pc, for example Gul’dan who could summon Archimond and Kil’Jaeden to the fight then gg (but SI has that op superpower weapon of mass destruction, so who knows).
If it were 1v1 without SI’s resources, I still think SI would win. With that superior use of the Force and lightning skills I can see warlock’s demons being dealt with pretty quickly or at least paralysed for the lightsaber strike. Warlock and SI are both dot classes with exception that SI also has heals and a bubble like disco priests. AND invisibility. So in my opinion, warlock is simply outclasses by SI’s abilities, which can counter warlock’s.
Storywise the SI ended in higher position of power than warlock ever did, which for me felt more fulfilling. Man, the Sith council was 1 step under the Emperor. If some shenanigan hadn’t happened, SI could have become the absolute ruler of the Sith Empire of old.