If being SR weak immediately makes a wall unviable...
then how come Lugia is one of the best walls in Ubers?
Yes Lugia does have a BST of 680, but it's an example that SR alone does not ruin a wall. Dragonite and Salamence can both wall pretty well despite their SR weaknesses (in fact thanks to Multiscale Dragonite walls VERY well, I know from experience). Gyarados can wall too (I have used it as such).
While an SR weakness is bad for a wall, true, it's not an instant death sentence. Hell, those Pokemon I listed aren't even optimized statistically for walling, but they can still do it anyway. Other factors come in for it.
The reason Tropious is NU is not because it's SR weak, but because it has bad defensive typing and its defenses are not high enough to completely offset that. It also, as you said, requires sun support to function properly, which is not present in tiers below OU. The reason Shuckle is NU is not because it is SR weak, but because it has no access to reliable recovery outside of Rest, no offensive prowess to speak of (barring Power trick, which suddenly turns it into the squishiest and SLOWEST thing imaginable), and terrible HP that offset its gargantuan defenses.
Furthermore, Tropius is far from outside the range of possibly getting an evolution, at 460 BST. For comparison, Magneton has 465 BST, Electabuzz has 490 BST, Magmar has 495 BST, Scyther has 500 BST and Porygon 2 has a very impressive 515 BST. All of these got evolutions. There is literally no reason for Tropius to not get an evolution.
Just letting you know that Eviolite does not boost BASE stats, it boosts the ACTUAL stats of the Pokemon in question. Otherwise, Chansey would have the same defense as Blissey when we all know that Chansey's physical defense far outstrips Blissey's. Not that this undermines you're point at all, just making sure that everyone knows that.