How to balance this
Let's say you get DCed and while you are gone your 4 allies accumulate 1000 exp and 600g
That then transfers to you on reconnect at a 100% the average so you get 1000/5 and 600/5 resulting in 200 exp and 102g on reconnect
It's a minuscule 20% of what your team accumulated while you were DC. This of course can be number tuned to a lower percentage to prevent abuse but the idea is you would not be entirely behind bust still noticeably weaker than you allies who didn't DC
This would give the support about what they would have gotten in lane exp wise but noticeably less gold and they lose them being there for pressure which puts the lane on a losing term to begin with with a 1v2 so the adc will be getting less gold and exp if the enemy knows how to abuse it
The gold income would be noticeably less than what the support would have got in lane
And let's say the top DCed, he ends up with much less gold and exp on return to game than if he stayed connected and in lane
DC doesn't just cost the team gold and exp, it costs the team pressure as well
The idea is the DC return will give them about what a support would get in lane for exp and gold, so even if the support DC and comes back when his adc is lvl 6 (assuming it happened at start of game) the support would get back to lane after reconnect at lvl 3-4 instead of lvl 1