I wouldn't feel bad. If you're unsure it's better to be safe. It looked like chlorosis to me but I'm still a novice and I wouldn't have expected to see that until the soil began to deplete. If they were quality seeds I would have sprayed them with an anti-fungal but since they were what they were, I think you made the prudent choice. They were likely to grow tall as well, so space could have been an issue. If I ever get a hold of any again, I'd love to see if I could train them low through LST and pruning, considering their resiliency. I've done some cool sh*t with rose bushes in the past. Wish I had pics still but the drive holding them got corrupted.
Yes, I will never underestimate Mex brick. I used to sell it back in the day and 4/5 times it would give anything I've smoked recently a run for it's money. If you consider that they're even stronger as sensi, and you'd probably harvest earlier, they'd have a good chance of being a most excellent cerebral stone.
I used to get this day-glow green Sexi-Mexi with around 95% fewer beans. Tasted like lemons, was sugar sweet, and had an incredible energetic high. Oh, I wish I had some of those seeds now. Remember that brick weed is just brick because they compress it for smuggling. It's no "one" strain.