Is Stake's rakeback better than a deposit match bonus?

Yes. Rakeback has zero wagering requirements, which means every dollar returned is real value you can withdraw immediately. A deposit match bonus with 40x wagering at 3% house edge is negative EV (you lose 20% more than the bonus is worth while clearing it). Rakeback at any percentage is always positive value. A 5% rakeback on a 1% house edge game effectively reduces your house edge to 0.95%.