All, I'm probably like you. Years ago bought a 420D after I paid someone too much to dig 1500' of water line and I still ended up doing the cleanup work. Now have accumulated a C6500 dump, a D4G, a 289D, a 299D3, couple of tractors, and so on. And my day job is still in an office. Burning diesel around the property keeps me sane.
But- I have an AFE disc mulcher. Based on input from this forum, I bought it for my own use over a drum mulcher, because it supposedly cost less to operate, and may be better in rocky ground. And we have a lot of rocky ground. What I've found in clearing is that unless you can actually get into the ground, the mulchers (or anything actually) will leave small stumps. And as Tones said, there is a definite learning curve to operating. The disc mulcher also seems to leave more stringy material, and there will be longer pieces dropped that are challenging to go back and chew up. When I cleared some hillsides (stuff been un bushhogged for 20 years) with the dozer, I ended up with large piles that I have not yet been able to burn. The little saplings were too small to push out readily as they just bent over, so each one had to be rooted out with the corner of the 6 way. I had more damage to the topsoil than I anticipated. In hindsight, I believe a root rake would have been better than just a dozer blade. This experience caused me to buy the mulcher.
But- your other mention is a brush cutter. I have a small cheap one I use around some tough spots. But I have seen some of the heavy duty ones running that sure look like they can get close to mulcher work, without all the cost. Thompson Cat in Nashville has one at their annual demo day, and you can knock down most things, run back over to cut up, and if there are no rocks you can backdrag to pulverize similar to a drum mulcher. My experience seems to show less of a learning curve than a mulcher. For use like I understand you have, I'd sure give thought to that and take the occasional large tree with your loader.
There was another point here- there are a ton of operators out there hiring out that kind of work, that frankly are probably working for cost. It is probably a pretty good chance you can hire it done for not much more than rental, fuel, and time. The land clearing forums on FB are full of guys complaining about folks operating at or below cost by guys who just financed a machine & went to work to cover the payment and fuel. But doing that takes the fun away from you. If you hire it out- as we all know- the price you pay may not necessarily correlate to the quality. I've paid too much for poor quality, and have sometimes been very pleased with the value I got from hired work.
Just my opinions.