That is correct, troop upgrade do not give XP. Neither do hero upgrades or wall upgrades. Only buildings and traps.
Even if the OP's idea were implemented, the fact that walls do not give XP would still make the system they want flawed. I think its fine the way it is. I feel I can compare my base to another fairly easily just by looking at the base and their profile (for the troops).
Park Diesel / TH9
As I implied, it will take more than removing XP from troop donations to make the XP gain remotely accurate enough to use as any kind of base measurement. The majority of the levels come from the time it takes to level up a building, and the XP gain for the time required isn't even linear. (reference http://clashofclans.wikia.com/wiki/E...ing_Structures) Many of the points gained are rather arbitrary. Plus you have XP gained from taking down Town Halls, and clearing obstacles; both of which you can do a lot of, but adds nothing to your base strength. Obstacles might add a marginal incress in base development if you use the gained gems on speeding things up, or save them for Builder's Huts and gain development faster.
And troop strength isn't even factored in. You get no XP from laboratory work on troops, nor XP from leveling up your Heros, even though those require a builder to do so.
The Level system is basicly an ego stroking device in the game. It is sadly almost a joke of a function, as it is a level system without a cause. Supercell may have had plans for it in development, but shied away from using it seriously for some reason at the last minute, and possibly never had time to pull it out of the game completely whenever it was rendered useless as a game mechanic, or expected to use it later, but never did.
The system has to be redone, numbers recalculated, and values balanced before it can be of any reliable use as some form of base strength measurement system. That effectively means removing the current system, practically wiping whatever levels and XP people have, and redoing all the numbers to give a proper level. That would mean looking at each base, and figuring out hundreds of XP values from each level of progress for the buildings in it, and then sum it all back up just for a simple, but accurate number. Granted, depending on the values used for each level for a building (and possibly wall), it won't take very long for each base, even for a mid-priced PC desktop computer it would take less than a second, and would take even less time with the servers they have powering this game. But we are talking about millions of bases here. The server would be down for possibly hours as it reviews and recalculates everyone. And I mean everyone, active and inactive bases alike.