Why are most cutters so crap?

[Tenson]

I need to route 9mm birch plywood. I didn't have a straight flute 6mm cutter so to get on with the job I went to B&Q and got one of their 'JCB' bits. I was only cutting 4.5mm per pass and it broke off like those cheapo bits from ToolStation etc.. that are £1 each. This was £8! I took it back and got another. Worked for about 1 hour and broke in the same way.

I took it back for a refund and get a 'Trade Range' Trend cutter from Screwfix which happens to have opened near me recently. Looks good, nice short 16mm cut length. It cut for less than 20mins and part of the TCT insert has come out.

Seriously, can't they make good quality anymore? I used to think Trend was good. Looks like only solid carbide for me now!

Is 6,000 mm/min at 4.5mm doc too much to ask for a 6mm cutter? It's only birch plywood! G-Wizard says it should be okay for a 'HP HSS End Mill'.