Locked? If you don't pay anything looks like you just get other heroes from playing(basic) and anything higher from the loot boxes/pinata's(which you seem to get while playing). So if you pay the $40, someone said you start with like solider, you unlock the other basic heroes just doing the story but things like rare and beyond heroes are just random from boxes/pinanta. Same with weapons.
So if you don't want to pay , just play a long and get stuff as you play. Since there is no pvp not like its going to hamper you at all. If anything people paying will help you progress faster if you group with them. Otherwise I don't see the "Win" aspect of the "p2w" argument, since it's not one world like a mmo and no pvp. So unless you pay or group with someone that did, it shouldn't effect you.
From what these guys are saying, you can pay a lot now just to get legendary heroes/weapons if you want, aka skip a lot of the start progress(still have to level them) or don't and just play to get them all eventually. Seems you can earn vbucks just playing and you use those to buy stuff from store(pinata etc) and then loot boxes are just from finishing missions. This one guy opened a pinata and got a mythic hero
I have a group of friends playing, we just all bought the $60 pack and will just earn the rest of the stuff eventually playing.