This will have multiple parts to the suggestion:
1. Reduce the overall number of badges per round. Server runs on badges and giving a 100 badge reward at 5% bonus is just overkill. Let people earn their keep and not get free rewards. This way BG will be running for longer during the week and not just for 5-7 rounds the day before WoE. Hoping to keep it at 50 badges without the % bonuses for Win and 30 badges for loss (Conquest). With 100% bonuses it'd be 100 badges.
2. Participation based badge payouts: This will be based on the number of minutes out of overall duration of that round.
Example: If TDM lasts 5 minutes (300 seconds),
People who started round can get 110% rewards, or a flat 3-5 badge payout for starting BG
Someone who joined and played on for at least 240 seconds (more than 80% duration) could get 100% of rewards
People who joined and played for at least 180 seconds but not exceeding 240 seconds (60-80% duration) could get 85% rewards
People who joined and played for at least 120 seconds but not exceeding 180 seconds (40-60% duration) could get 60% rewards
People who joined and played for at least 60 seconds but not exceeding 120 seconds (20-40% duration) could get 40% rewards
People who joined and played for at less than 60 seconds (less than 20% duration) could get 20% rewards
3. Support classes deemed essential to BG will receive 2-5% more rewards if they are the only or one of two supports of that class within their team. This list comprises of Minstrels, Gypsies, High Priests and Scholars. This reward will only be activated when BG is running less than 20 vs 20. This encourages people to re-roll into classes needed for BG and not farm BG with just an ungeared/no pots linker.
Example: If a team has 10 players - 2 DD HWs, 1 DD Creo, 1 Soul Linker, 2 FS Scholar, 1 Minstrel and 3 Gypsies, the FS Scholars, and the Minstrel will get extra rewards.
This addresses the problem of last second joiners AND encourages people to start BG or join BG early instead of joining midway through/when ending (which is about 50-60% of BG participants right now).