Though I've only played pokemon competitively since the end of 5th gen I do have some experience with full BP chains. When i first built my BP team I had never at that point seen or heard of full BP teams. I started with gliscor(rock polish, taunt, subs), mew(w/weakness policy, barrier, amnesia), togekiss(fairy, nasty plot), m-scizor(swords dance) drifblim as my lead(w/weakness policy, unburden, stockpile) and espeon(magic bounce, stored power). This team did quite well for me to start with, definitely not OP, but over time i saw more and more flaws and missed out potential. So I thought switch togekiss with sylveon and though this did help it was never "unbeatable". Then i switched scizor for vaporeon as scizor rarely did anything. Better but still nothing that couldn't be dealt with. I was happy with my team. I didn't feel like i wasn't thinking when i was playing I just felt like i was thinking differently. Biding my time, making crucial switches with no room for error. It was fun. I had been advised by many people to put scolipede on my team for obvious reasons. Now, i had thought of scolipede but passed as i wanted my team to be pokemon i personally liked but eventually i had to give it a try. Scolipede replaced drifblim and shit got real. I was unstoppable. I couldn't believe just how big of a difference this bug made. Even with mew as a big weak point i was still get 6-0's allover the place. Essentially what i'm getting at is that imo scollipede is the pokemon that makes full BP chains so very difficult. Not espeon or sylveon or any other and though it really is a combination of pokemon scollipede is what made this such a problem. What i find so OP about scollipede on a BP team is that normally if you mess up the chain, your done, gg, accept defeat. but with scollipede it is very easy to start all over again and build speed and ideally defense. I love my BP team but even I have to admit that with scollipede its just unfair. I see why banning speed boost scollipede seems unfair as he is viable on his own on other teams but I feel it would be the best solution to this problem. Full BP teams are a legit play style imo. It's a risky play style without scollipede that requires analyses of your oponents team and proper prediction and maintenance of your acquired boosts but i'm sure someone will point out many, many flaws in what i've said.