But if you don't get a T70 out in optimal time then P4 shows up like 30 seconds later and kills it immediately.
This is true for a lot of units. There are a handful of units that are useful throughout the game, but most need to be edged in at the right time* or they're completely worthless.
T70 is one of the most obvious examples. 55 fuel vs 85 fuel for T-34: The 30 fuel difference is nearly meaningless on the game's timeline, especially if you factor in that any initiative lost waiting the couple of extra minutes for the T-34 can be potentially completely reversed into you winning the game (or at least you'll be able to hold vs. the inevitable PzIV-led offense). Considering that the T70 is completely shut down by every grenadier with a faust and that Relic removed its only redeeming feature - squishing infantry - it's a fair to call it useless. Also, Their main gun is also weak that the german doesn't even need bother with driving his light vehicles out of the way. Finally, as others have mention already, it doesn't scale past the first enemy tank (which comes out maybe 3-5 minutes later) so why ever bother building it?
German T4 is equally useless. They cost too much and they have no target on the battlefield. Yes, the BBaer has some good lulz-potential shooting at Paks, but 3 PzIV cost as much and are better at being present on the battlefield. The Panther is just entirely useless, because it has no targets and going T4 for the Rocket Launcher is being decadent at best, gibbing infantry can be done cheaper and more effective with less investment.
* and we all know that in any battle that deserves the name, they'll never be 'on time'.
And then there is the issue with the Paks. I really want to like them and they've gotten better but the fundamental issue with them is still that they factually are two units, themselves + a babysitter and they require an extra bunch of micro to not die to the first angry stare by the enemy. Consequently a lot of involvement required. Considering I can just shove another Panzer on A-Move into the opponents rear area for great dillema, the only real reason to ever build a Pak is if you're low on fuel. Like a dumb german skipping T3 and then complaining why Relic has the audacity to allow 5 T-34 to take out his single Panther. But I disgrees: Pak: micro-hell. Tanks: Can defend vs. armor on autopilot while my attention is elsewhere, while simulatenously being able to pressure the offensive. For something that passive, a Pak needs to Pak a bigger punch imo. What would also help a great deal is if tanks couldn't drive around like they own the damn place, in general there is only one thing a tank fears: other tanks. And that explains most of the gameplay we see even at high level.
There are a lot of 'sloppy' units (in the sense that their potential impact they can have on the battlefield hasn't been balanced properly vs. their effectivity) in the game and I think if Relic would take the time to straighten those out, we could play a game that is overall more stategically diverse and exciting to play. Don't even need new bunkers or sandsacks.