Edit: Basically the same as NCL4701 said above...being in TN, it's not surprising we have similar topography and needs.....my original reply below as well.
You can make this comment over and over for each step up. At some point it's big enough

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I see your point but I'd suggest looking at it from another perspective -- the argument you make from the L4701 to MX is the same as one can make from the L3901 to the 4701. The extra 45% lift capacity for the 4701, extra weight, and bigger frame were totally worth it. Another step up would have been too much IMO. Could it work? Sure. Is the MX a good deal compared to the 4701? Absolutely. But it already feels tight in the trees - the extra width and length would make it even more difficult to turn around and work the grapple, mower, and rake in tight spaces.
And in truth, the width is a non-starter because the rear wheels are adjustable for width. It makes no difference to me what folks decide to buy, and it's a good thing that you're happy with the L, but I really don't see how an MX would be a problem for someone who likes and has an L.
Absoultely agree it's worth looking at both. But I don't think it's fair to expect that the MX is the right choice for 100% of buyers.