DE have stated that they want MR to be a balancing point this is true. However if you look into the damage outputs of weapons even after the balance pass, you'll see that many of them do not perform at a level which justifies their current MR requirement. The Opticor being one of the most notably over-MR'd weapons in the game.
Also in the case of the Prova Vandal, which also share's its MR rank with its original, its a stronger weapon in every aspect. However melee has yet to have its balance pass so I expect this to change. This does not mean that there should not be further balance passes for firearms, as the last pass missed several weapons, and the introduction of kitguns at their current power level makes the balancing decision on others weapons made worse or left to atrophy in the balance pass all the more questionable.
In this case the Opticor Vandal is not the same type of weapon as the original, does it have a higher DPS? Certainly, but the people who like the original have been waiting years for an upgrade, not a side-grade. Would you really tell those people to wait several more years to get a better version of the weapon they like? Or would you rather everyone gets the thing they want out of the current one?
In my opinion the Opticor would fit neatly into the MR power 'scale' at rank 8-10. With MR 10 being very generous as its crit chance is a complete coin toss. Now of course you could bring up 'rivens' but I'll be quick to remind you that DE have stated themselves that warframe content will not be balanced for rivens, rivens are meant to add more variety to the gameplay as-is, not act as a band-aid to fix everything or as an excuse for poorly balanced weapon stats.
36% Crit is not insane at all.
20% Crit +150% = 50% Crit, 1-1 coin toss [1/2]
24% Crit +150% = 60% Crit, 6-4 coin toss [3/5]
28% Crit +150% = 70% Crit, 7-3 coin toss [7/10]
32% Crit +150% = 80% Crit, 8-2 coin toss [8/10]
36% Crit +150% = 90% Crit, 9-1 coin toss [9/10]
I dont think I need to remind you that most charge based weapons (i.e. bows) have higher crit stats when fully charged. For example
Charged Critical Chance Values
MK1-Paris, Paris: 30%
Cernos Prime, Rakta Cernos: 35%
Paris Prime: 45%
Dread, Lenz: 50%
Sniper Rifle Critical Chances
Vulkar, Vulkar Wraith: 20%
Snipetron Vandal: 28%
Rubico, Snipetron, Vectis Prime: 30%
Rubico Prime: 38%
Lanka: 25% (+20-50% depending on zoom, 45-75%)
Considering the AoE of the Opticor has rapid falloff within its radius, toting it as an 'AoE' weapon is rather disingenuous. Its primarily a pin-point high damage weapon. Similar to Bows and Sniper Rifles in that regard. Mind you even if this alt-fire were added it would still be rightfully outpaced by purpose-built pin-point weapons like sniper rifles, but would offer the massive single-shot damage people who liked the original were looking for in a variant. So what's the problem here?