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Disrupt is really the concern I think, yeah. Shard wall being limited doesn't matter if disrupt isn't limited (stonewalls are almost as good as shardwalls with disrupt out of the equation). Disrupt being limited would definitely change the meta a lot. Not really sure if for better or for worse - personally I'd be fine with it, but I'm also fine with the status quo in regards to wall availability.
A thought if they did become obelisk bound: it may be worth making them both red shard exclusives. Red shards are actually somewhat bad now (I actually value blueshards more highly, my pouch is full of reds I never use) since you burn through blues with leylines and such. Making wall/disrupt red shard exclusives and unique I think I'd be mostly fine with, as with shard decay and such you'd not be able to spam them endlessly as you would be able to if they remain blue due to the number obtained per successfull shardfall. Shard combine would potentially pose a problem still, though.
I suspect shardwalls in raids would be offset by cannons auto breaking them. Of course people could just opt to have 0 cannons and shardwall, but I think that'd be a pretty bad trade. If people did go that route class composition would become more important, since you'd want someone who can leap/flip over walls to follow. Again, good or bad, depending on your preference (all hail our new berserker overlords).
Agree shard mark isn't worth it, for the reasons you stated.
Reflections are a bad mechanic in general, both in teams and one v one, because we don't have much of the historical counters anymore (mass passives). All for nerfs. They were on my list too.
That said, the champion strat doesn't work against champion teams, because you have two choices: deny faith or deny yourself starbursts. If the enemy team is champion and you get burst, you lose champ, then they get faith on the true kill. Slightly mitigates, but not really a solution (unless you're all inhumed or something).