I think the best solution since we already have levels we move up at and level targets which unlock increased item attributes would be to simply introduce a level cap. For example gold 3 4 & 5 have a item cap of level 28. This way no matter if the player has level 34+ maxed items they only enter the match with these items with a max value of 28. This can also be done at silver levels with a level cap at 11 and 22 or whatever would make the most sense.
This in effect would even the playing class at each level and give no benefit for people to stay in lower tiers farming easy wins.
I think the developers are aware of this however i suspect they are happy with people staying in the certain lower levels and being in these classes year in year out, to keep the player base cross section active among all levels. I suspect with the dwindling player base if everyone progressing to level 50 there would not be enough players at the lower levels to match with for newer players and in effect the game would die.
Keep in mind the developers really need these level droppers. Yep thats right i suspect they indirectly bring in more revenue to the game than any other players!
How much do you think a platinum player spends on the game on average? I assume a lot less than someone just starting coming into silver 2 getting smashed by these level droppers, thinking that dropping $100s on gold and gun-bucks to try and complete with these players only to bitterly disappointed. It's human psychology and at the end of the day all the devs care about is profit not our overall playing experience. I suspect nothing will change.