Those attacks are almost impossible by the current Design ..,

As the harvest clubs can increase their harvest power by increasing their number of members it will be almost balanced forever as more and more people joining a specific club increasing it's harvest power to take over the most incentives .,
that incentive will be divided into more people leading to equilibrium state at the end of the day

Let's say we have a greedy club leader having 25% of all signals and total number of addresses that can provide signals are 400k addresses ,
100k Signal TXs / 100k club member ., so if they have 25% of all network votes the rewards will be payed to the club members automatically and equally so that will make the rewards almost equal to another club which owns 1% of signals and having 1% of the rewards .


Again after people switch from the club to another the incentive which is payed to the club leader will be decreased as his number of signals will decrease at the same time the other clubs's signals will increase leading again to the point where he only gets what he deserves

Nope !!

People won't give a potato who is the club owner as long as he pays *not even manually * And that voting system is a already a core feature of TAU .
and that timer and self destruct is a good idea TBH

Although the current system isn't flawless and have room for some manipulations with TX spam and mass addresses owners .. all that can be fixed if a number of TAUs will be locked for a certain amount of blocks for each new address and for each created TX  "not forever as XRP as that's called theft "and will still allow painless micro-payments .
Also the harvest power should be automatically decreased if the node isn't always online or under-performing .