1. I think lvl requirements on items in the shop turned obsolete after the introduction of rank-based matching system.
I got to rank 3 as a lvl 22, buying Item boxes. Now I got some good items and can compete reasonably well between ranks 3-4, yet, the win to loss ratio of 3:1 is not exactly much fun. I got enough Heat and Energy modules and think I could better use some Armor Platings. Yet, the ones I can get at lvl 22 are too ineffective at this rank and I don't get any higher lvl ones from the boxes. Getting to lvl 30 is also considerably prolonged because of the 3:1 win to loss ratio and so this situation gets frustrating.
So I ask developers to remove the lvl requirements in the shop.

2. Also - the rank-based matching system is not nice for leveling up at any rate and I think in the current setting it will be reasonable if lvl 30 could be gained just by completing the normal campaign.

Yeah, I agree. I got a lot of Mythical weapons early on from gold item boxes in the campaign, so I climbed the rank ladder pretty fast. However, when I got to rank 3, I got a ton of losses from level 30 mechs who had much superior torsos and weapons. Now, I just sort of sit between rank 5 and 3, because I can't buy any better weapons.