I've got Horizons but not been doing any real combat (certainly not PvP) since Horizons. Mostly been blasting round on or above the surface and doing non-combat CG's.
So not a big issue to me at all but 30% better weapons only if you have Horizons that will be seen as Pay to Win, in fact it is Pay to Win. You pay Money you get access to better weapons that's what P2W is.
Strictly speaking, yes. But you need multiple extremely rare (type 5) materials, and the boost only works until you reload. To give an impression, I have, in total three t5 materials after over a dozen hours of driving around. I can also escape to a planet where you cant chase me. You'd have to limit things very much to prevent this.