You'd be right. It would need to dwell for considerable time on the same part of the tank's armor to have any meaningful effect, and even that would rely on slow, inefficient heating as a mechanism. (Assuming a rather improbable 100% kinetic energy transfer from a 60kW beam, that equates to about three .50 BMG rounds per second from contact range. That's a big round, but not big enough to have a significant effect on tank armor.)
To address another commenter's point, it would not set off explosive reactive armor (ERA). While I don't have detailed information on the ERA compositions in common use, the constraints at hand effectively necessitate the use of relatively insensitive plastic explosives, broadly similar in characteristics to the well-understood C4. Such explosives require a shock wave, provided by a special device or (in the case of ERA) by the impact of a shaped charge, to detonate; heat and fire will not set them off. (Vietnam-era American soldiers burned pieces of C4 from Claymore mine charges as cooking fuel. The smoke was toxic, but that was the only danger.)
You need a composition like this for ERA because it is not an actively controlled system. It's not as though there is a computer in the tank which detects an impact and detonates the corresponding ERA segments; the physical processes of such impacts play out far too quickly for such active control to work. ERA therefore has to work on a purely physical basis if it's going to work at all, and that means you need to use an explosive susceptible to detonation on impact. But you don't want an explosive that's very sensitive to impact, or to heat or fire, because you don't want to waste ERA or unnecessarily endanger infantry operating near the tank. (ERA's dangerous enough already that way without giving it a hair trigger!)
So it's already not all that plausible that a beam like this might transfer enough energy, even on direct impact with a mass of such explosive, to set it off. But the impact won't be direct, because ERA isn't constructed of bare explosive blocks; there's always going to be a layer of metal, not armor but still relatively thick, between the explosive and the outside environment. This structure would intervene between the explosive and the beam, and would dissipate the transfer energy as heat. That might eventually set the underlying explosive on fire, but, for the reasons we've already covered, it would not cause a detonation.
