I think the opposition parties, especially the stronger ones, should contest as many seats as they could, no need to worry about 3-corner fights.
Then each party will know how much support it has. The better parties will likely to attract more capable people. I think this is one way for a strong opposition to emerge. It is also better for whatever talents they could get to be in one party rather than spread out in ten parties.
The opposition seems to think that people who want to vote for the opposition will support any opposition party. If this were so, doesn't it means all the opposition parties have similar ideology and manifesto. Then they may as well come together to form one party.
Assuming 60% want to vote for the opposition. Of this 60%, maybe only 30% will vote for any Tong, Yacob or Kumar. The others have their own mind what oppositions they want.
For example, you support FLOP (Frannxis' Love Opera Party) but it is not contesting in your ward. Since you do not like the other opposition party, you might vote for the ruling party or you may spoil your vote.