Is it a good idea?
More armor obviously means less damage from the enemy ADC but i'm worried that supports will hit harder in that case.
What do you guys think?
And any other suggestions about what I can replace my MR blues with? I don't have a problem with them but I feel like there might be a better option.
Not worth it...especially if you happen across an opponent picking a Corki.
AD reds, health yellows, five mr blues, four attack speed blues, two attack speed quints and one armor quint.
Is it a good idea?
Ehh - if you pick a stat for runes that they don't specialize in, you're running with around half-power for that stat. Really sub-optimal, especially when you consider the longer you survive the more damage you deal, and almost every stat in lol scales exponentially with other stats, while only linearly with itself. 100 base AD + 100 AD + 100% AS + 100% crit +50/50% armor penetration means 1600 DPS, where 100 base AD + 100 AD + 100 AD + 100 AD +100 AD = 500 DPS. Not picking a stat a rune type specializes in is not a good idea.
MR glyphs are nice because Glyphs specialize in MR, where Seals specialize in armor.
MR glyphs are also nice because the other things glyphs specialize in are largly useless for most marksman. Additionally, MR per level was extremely handy on marksman due to most mages having a 100%-->0% combo, and most skills capable of hitting marksman being ranged, magical things - often causing them to take more than 50% of their damage as magic damage. Tie into that most champions, marksman or not, get around 75 armor at 18 - where all marksman start with 30 MR and don't get any more, and MR per level is pretty handy even when damage is pretty even.
Granted - if the enemy team is really AD heavy (Nasus, Lee Sin Zed, Lucian, Janna) and you know about it because Draft you're probably better off running a few extra half-powered armor runes than MR runes, but I wouldn't recommend just swapping out MR runes for weaker armor runes in general. Ending with 75 armor and 30 MR makes MR on marksman more important than armor in 50/50 phys/magic environments as-is.
Also, for the lanning phase - it's important to consider supports are the strongest champions in the game without items, and when you're starting out - nobody has much in the way of items. Might want a bit of MR for when that support starts getting solid bases.
