Sounds odd that you can’t even lock up a wheel with the DB5’s – although they are pretty low down the Sram range.
I’ve had the mk1 Guide RS and never boiled anything even on a full uplift day at BPW. I’m only about 80kgs though and riding kit doesn’t add much weight. That was on 160mm rotors at both ends and sintered pads.
Now got the mk2 Sram Guide R with 200mm/180mm rotors and they feel more powerful than the RS I had. Was worried the lever wouldn’t feel as good without the swing link and bearing pivot that the higher models have got but hasn’t bothered me in the slightest whilst out riding. Only had them for a couple of rides and the worst I’ve been down so far is the Pedalhounds DH at Cwmcarn.
Another thought is why not try the Sram Guide RE? New out and meant for e-bikes – has the Guide R lever but the Code DH calliper – might be just the ticket with say 200mm/180mm centreline rotors.
If the levers fit alright around your current shifters then you hear good things about Shimano Zee / Saint.