If they're the sort to appreciate straight talk, plainly state you feel the team lead is doing more harm vs delivering value to the company. Otherwise back into it from "There are some issues with the way things are working that I've noticed..."
Make sure to include you're not the only one who feels this way. But certainly don't name or get overly specific with the others you've talked to. I'd simply suggest the founders reach out to {these groups} to get their opinions.
End with the work environment created by the team lead is directly causing you to look for other opportunities. (Hint: go ahead and start interviewing and have semi-serious job leads before this talk)
Remind them of what you feel you've done: never overestimate their knowledge of who actually did / does what.
State that you like(d) working at the company, found the problems interesting, and loved what you felt you and the founders had done ("together!" Be generous, and appreciative of whatever they did to keep the company a going concern while technical problems were solved).
If they do come back with an offer, as GP cautions, make sure you don't agree to any "company will make things better in an unspecified manner, in exchange for ensuring you work there another X years" forms of compensation.
If you do feel the offer is too vague ("We'll talk to team lead"), thank them for that, but push back and remind them that you've already been dealing with this for X months and are going to need a firmer commitment to change things.
Then see where it goes. Anything worth getting it worth asking for, especially if you have concrete other options.