I was going to cheekily suggest a rheostat, but you've already tried (assuming wirewound) power resistors and they were too inductive. A rheostat wouldn't fix that.
If spiffy equipment is not available, there are non-inductive power resistors available. They typically come in a package that needs to be mounted to a heatsink. I recently bought some resistors like this for a test at work; they were effectively TO-220 case parts and rated to 30W. The nice thing about these kinds of resistors is they tend to have isolated packages, often ceramic backed.
Here's an example of a 100W 100Ω resistor in TO-247. Datasheet says 11.7nH inductance.
https://www.digikey.com/en/products/detail/riedon/PF2472-100RF1/2447861https://riedon.com/resistors/view/to-247-power-film-resistors-pf2470Worth saying twice that you'll need a heatsink.
EDIT: The trouble with E-Loads is they pretend to be resistors (CR mode) by modulating the gate inputs to a bank of power MOSFETs with a control loop. It would have to be a screaming fast control loop to make a power MOSFET look like a programmable resistance to a 100kHz square wave. You might be able to set up a "dumb" essentially open loop current sink with a large power BJT, an emitter resistor, and a voltage source to set the base-to-ground voltage. I know it's not a resistor, but it is a programmable open loop current sink.
EDIT2: Resistance wire of a suitable diameter bent into a non-inductive shape (squiggle line) that minimizes path length. Mount it on a high temperature substrate and tap into the wire at various points with a clip that can handle the current.