Before deciding whether the DK35 is "too heavy for mowing" you really need to decide what you're going to mow, how you're going to do it, what do you anticipate the conditions to be and last, but not least, how fussy are you about the end result. If you want your lawn to look like a golf course then the DK35 is too heavy.
Here's an example, from back 50' - 75' my lawn looks great. On closer inspection, there is a variety of weeds and the ground is not perfectly flat. Using round figures my JD 3320 weighs 3,000, the FEL 1,000, the MMM 450 and the BH 1,150. so with a full tank of gas + myself the whole package is getting close to 6,000 - quite a bit heavier than the DK35. I have turf tires and rarely remove the FEL and / or BH. I'm probably getting some soil compaction, but not so much I can't live with it.
Another consideration - look at the FEL lift limits for weight and height. What is the maximum load you think you might ever want to lift? Around here they have one cubic yard bags of black topsoil. Being able to lift and move one of those was a criteria for me. Would you ever want to lift a bucket of dirt or anything and load it into a dump truck - how high is that?
Tonight for example, we lifted a helm seat into a boat sitting on a trailer. The side of the boat was somewhere between 7' - 8'. In this case the weight was minimal, but height was important.
Would you ever want / need a BH or some other implement? You'll never find one machine that is absolutely perfect for every job, but if you take a look at potential work and set minimum standards for each job, that exercise will quite likely point you towards the tractor size that's the best compromise for you.