On the topic of four castes, I have noticed no one caste is proficient in everything. All have their positive and weak points.
Brahmins+Khatris are very good in intellect, command over languages, business sense, but lack in technical knowledge and artisan skills. With my own eyes I've seen they are literally unable to use a screwdriver.
Jatts excel in health, stamina, stick up for each other, (over)confident. But education lacking. Big Ego. Impatient.
Lohars, Ramdasia, Tarkhans etc excel in artisan skills requiring use of hands, fine motor skills (includes sewing etc), patience, technical knowledge. Weakness include lack of business sense, and like most engineering types reserved/not great communicators.
Point is caste discrimination is mostly based on looking only at the negative aspects of each group and ignoring the positives. Might be helpful if we change perspective and see what we have to gain by marrying into another caste. The more we mix up the more likely we will produce offspring that have all the positives of the four castes in one person which is what Guru-ji wanted. A kind of superhuman! Think about it, a Singh who is a CEO, intelligent, physically fit, and can fix his own car! Ultimate Alpha!