My problem with a HXP locked per type/model of chassis is this:
I have lots of mechs. LOTS. I'm a collector, so I don't sell many. And of course I have my preferences, so I prefer to play with certain mechs. I made most of my XP on those. Still. I wanted to master most of them (even unused) so I bought much MC to convert it to GXP. I also have hundreds of modules. So far so good, that was all my choice. I know, I'm a whale but I don't mind.
But now this comes up... When I look at the test server now, most mechs I own have between 30.000 and 50.000 XP. Enough to unlock about 33 nodes. In terms of capability does not even nearly equal the level of 'mastered with mods' mechs I have now. In order to get (even just mu most used mechs) back to the level they are now, with mods and all, I would have to get about 50-60 nodes based on the mech.
C-bills are actually not the issue, I have so many mods I will drown in C-bills. The mods were all bought from C-bills earned in game or gained through packs. But all that XP from my most-used chasssis that I converted into GXP went to the other less-used chassis, mostly to master 1 and sometimes to master them all. Since that is now all locked into individual models/types, the only way to get just my most used mechs back to master is to... buy even more MC to turn it back into GXP.
I might even accept that if it was the same for everyone, but it isn't. People who play just as much as me but only have a few mechs they use a lot (some with tons of XP on them) and who never bought a mech or MC, will most likely be able to master their handful of mechs with relative ease. All their XP are on I on the other hand will be stuck with 170+ mechs that have 30-40 nodes unlocked. And if I wanted to sell them (I still own them) I'd even lose access to their HXP.
I think it's not right fo me to have to pay MC to convert HXP to GXP, when I already bought so much MC to redistribute it in the first place. It's like having to pay tax over the same earnings twice...